Supplemental Indenture dated as of March 1, 2019, between Public Service Company of Colorado and U.S. Bank National Association, as successor Trustee, creating $400 million principal amount of 4.05% First Mortgage Bonds, Series No. 33 due 2049

SUPPLEMENTAL INDENTURE NO. 29, dated as of March 1, 2019, between PUBLIC SERVICE COMPANY OF COLORADO, a corporation duly organized and existing under the laws of the State of Colorado (hereinafter sometimes called the “Company”), and U.S. BANK NATIONAL ASSOCIATION, a national banking association, as successor trustee (hereinafter sometimes called the “Trustee”) to Morgan Guaranty Trust Company of New York under the Indenture, dated as of October 1, 1993 (hereinafter called the “Original Indenture”), as previously supplemented and as further supplemented by this Supplemental Indenture No. 29. The Original Indenture and any and all indentures and all other instruments supplemental thereto are hereinafter sometimes collectively called the “Indenture”.

Recitals of the Company

The Original Indenture was authorized, executed and delivered by the Company to provide for the issuance from time to time of its Securities (such term and all other capitalized terms used herein without definition having the meanings assigned to them in the Original Indenture), to be issued in one or more series as contemplated therein, and to provide security for the payment of the principal of and premium, if any, and interest, if any, on the Securities. The Original Indenture has been recorded in the office of the Clerk and Recorder of each county in the State of Colorado in which the Company owns real property that is used in or in connection with the Electric Utility Business, as more fully set forth in Schedule A hereto.

The Company has heretofore executed and delivered to the Trustee the Supplemental Indentures referred to in Schedule B hereto for the purpose of establishing various series of Securities and appointing previous successor Trustees.

The Company desires to establish a new series of Securities to be designated “4.05% First Mortgage Bonds, Series No. 33 due 2049” such series of Securities to be hereinafter sometimes called “Series No. 33”.

The Company has duly authorized the execution and delivery of this Supplemental Indenture No. 29 to establish the Securities of Series No. 33 and has duly authorized the issuance of such Securities; and all acts necessary to make this Supplemental Indenture No. 29 a valid agreement of the Company, and to make the Securities of Series No. 33 valid obligations of the Company, have been performed.

Granting Clauses

NOW, THEREFORE, THIS SUPPLEMENTAL INDENTURE NO. 29 WITNESSETH, that, in consideration of the premises and of the purchase of the Securities by the Holders thereof, and in order to secure the payment of the principal of and premium, if any, and interest, if any, on all Securities from time to time Outstanding and the performance of the covenants contained therein and in the Indenture and to declare the terms and conditions on which such Securities are secured, the Company hereby grants, bargains, sells, releases, conveys, assigns, transfers, mortgages, pledges, sets over and confirms to the Trustee, and grants to the Trustee a security interest in, the following:

Granting Clause First

All right, title and interest of the Company, as of the date of the execution and delivery of this Supplemental Indenture No. 29, in and to property (other than Excepted Property), real, personal and mixed and wherever situated, in any case used or to be used in or in connection with the Electric Utility Business (whether or not such use is the sole use of such property), including without limitation (a) all lands and interests in land described or referred to in Schedule C hereto, and all right, title and interest of the Company in goods, fixtures or improvements located on those lands, if any, described or referred to

1

in Schedule D hereto, provided that the Lien hereof shall not extend to or encumber the fee owner’s interest in any land or interest in land in which the Company holds only a leasehold interest; (b) all other lands, easements, servitudes, licenses, permits, rights of way and other rights and interests in or relating to real property used or to be used in or in connection with the Electric Utility Business or relating to the occupancy or use of such real property, subject however, to the exceptions and exclusions set forth in clause (a) of Granting Clause First of the Original Indenture; (c) all plants, generators, turbines, engines, boilers, fuel handling and transportation facilities, air and water pollution control and sewage and solid waste disposal facilities and other machinery and facilities for the generation of electric energy; (d) all switchyards, lines, towers, substations, transformers and other machinery and facilities for the transmission of electric energy; (e) all lines, poles, conduits, conductors, meters, regulators and other machinery and facilities for the distribution of electric energy; (f) all buildings, offices, warehouses and other structures used or to be used in or in connection with the Electric Utility Business; (g) all pipes, cables, insulators, ducts, tools, computers and other data processing and/or storage equipment and other equipment, apparatus and facilities used or to be used in or in connection with the Electric Utility Business; (h) any or all of the foregoing properties in the process of construction; and (i) all other property, of whatever kind and nature, ancillary to or otherwise used or to be used in conjunction with any or all of the foregoing or otherwise, directly or indirectly, in furtherance of the Electric Utility Business;

Granting Clause Second

Subject to the applicable exceptions permitted by Section 810(c), Section 1303 and Section 1305 of the Original Indenture, all property (other than Excepted Property) of the kind and nature described in Granting Clause First which may be hereafter acquired by the Company, it being the intention of the Company that all such property acquired by the Company after the date of the execution and delivery of this Supplemental Indenture No. 29 shall be as fully embraced within and subjected to the Lien hereof as if such property were owned by the Company as of the date of the execution and delivery of this Supplemental Indenture No. 29;

Granting Clause Fourth

All other property of whatever kind and nature subjected or required to be subjected to the Lien of the Indenture by any of the provisions thereof;

This Instrument shall constitute a financing statement under the Colorado Uniform Commercial Code (the “UCC”) to be filed in the real estate records, and is filed as a fixture filing under the UCC covering goods which are, or are to become, fixtures on the real property described herein, in the Original Indenture and all supplements to the Original Indenture;

Excepted Property

Expressly excepting and excluding, however, from the Lien and operation of the Indenture all Excepted Property of the Company, whether now owned or hereafter acquired;

TO HAVE AND TO HOLD all such property, real, personal and mixed, unto the Trustee, its successors in trust and their assigns forever;

2

SUBJECT, HOWEVER, to (a) Liens existing at the date of the execution and delivery of the Original Indenture, (b) as to property acquired by the Company after the date of the execution and delivery of the Original Indenture, Liens existing or placed thereon at the time of the acquisition thereof (including, but not limited to, the Lien of any Class A Mortgage and purchase money Liens), (c) Retained Interests and (d) any other Permitted Liens, it being understood that, with respect to any property which was at the date of execution and delivery of the Original Indenture or thereafter became or hereafter becomes subject to the Lien of any Class A Mortgage, the Lien of the Indenture shall at all times be junior, subject and subordinate to the Lien of such Class A Mortgage;

IN TRUST, NEVERTHELESS, for the equal and proportionate benefit and security of the Holders from time to time of all Outstanding Securities without any priority of any such Security over any other such Security;

PROVIDED, HOWEVER, that the right, title and interest of the Trustee in and to the Mortgaged Property shall cease, terminate and become void in accordance with, and subject to the conditions set forth in, Article Nine of the Original Indenture, and if, thereafter, the principal of and premium, if any, and interest, if any, on the Securities shall have been paid to the Holders thereof, or shall have been paid to the Company pursuant to Section 603 of the Original Indenture, then and in that case the Indenture shall terminate, and the Trustee shall execute and deliver to the Company such instruments as the Company shall require to evidence such termination; otherwise the Indenture, and the estate and rights thereby granted shall be and remain in full force and effect; and

THE PARTIES HEREBY FURTHER COVENANT AND AGREE as follows:

ARTICLE ONE

Securities of Series No. 33

There are hereby established the Securities of Series No. 33, which shall have the terms and characteristics set forth below (the lettered subdivisions set forth below corresponding to the lettered subdivisions of Section 301 of the Original Indenture):

(a) the title of the Securities of Series No. 33 shall be “4.05% First Mortgage Bonds, Series No. 33 due 2049”;

(b) the Securities of Series No. 33 shall initially be authenticated and delivered in the aggregate principal amount of $400,000,000. The Securities of Series No. 33 may be reopened and additional Securities of Series No. 33 may be issued in excess of the amount initially authenticated and delivered, provided that such additional Securities of Series No. 33 will contain the same terms (including the Stated Maturity and interest payment terms), except for the public offering price, issue date, and if applicable, the first interest payment date, as the other Securities of Series No. 33. Any such additional Securities of Series No. 33, together with the Securities of Series No. 33 initially authenticated, shall constitute a single series for purposes of the Indenture and shall be limited to an aggregate principal amount of $1,000,000,000;

(c) interest on the Securities of Series No. 33 shall be payable to the Persons in whose names such Securities are registered at the close of business on the Regular Record Date for such interest, except as otherwise expressly provided in the form of such Securities attached as Exhibit A hereto;

3

(d) the principal of the Securities of Series No. 33 shall be payable on September 15, 2049, the Stated Maturity for Series No. 33;

(e) the Securities of Series No. 33 shall bear interest at a rate of 4.05% per annum; interest shall accrue on the Securities of Series No. 33 from March 13, 2019 or the most recent date to which interest has been paid or duly provided for; the Interest Payment Dates for such Securities shall be March 15 and September 15 in each year, commencing September 15, 2019, and the Regular Record Dates with respect to the Interest Payment Dates for such Securities shall be March 1 and September 1 in each year, respectively (whether or not a Business Day);

(f) the Corporate Trust Office of U.S. Bank National Association in New York, New York shall be the place at which (i) the principal of, premium, if any, and interest, if any, on the Securities of Series No. 33 shall be payable, (ii) registration of transfer of such Securities may be effected, (iii) exchanges of such Securities may be effected and (iv) notices and demands to or upon the Company in respect of such Securities and the Indenture may be served; and U.S. Bank National Association shall be the Security Registrar for such Securities; provided, however, that the Company reserves the right to change, by one or more Officer’s Certificates, any such place or the Security Registrar; and provided, further, that the Company reserves the right to designate, by one or more Officer’s Certificates, its principal office in Denver, Colorado, as any such place or itself as the Security Registrar;

(g) the Securities of Series No. 33 shall be redeemable at the option of the Company at any time prior to March 15, 2049 (which is the date that is six months prior to the Stated Maturity (hereinafter called the “Par Call Date”)), in whole or in part, at a “make whole” redemption price equal to the greater of (i) 100% of the principal amount thereof to be redeemed or (ii) the sum of the present values of the remaining scheduled payments of principal and interest on such Securities to be redeemed that would be due if such Securities matured on the Par Call Date (excluding the portion of any such accrued and unpaid interest to but excluding the Redemption Date), discounted to but excluding the Redemption Date on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 20 basis points, plus, in each case, accrued and unpaid interest thereon to but excluding the Redemption Date. At any time on or after the Par Call Date, the Company may redeem the Securities of Series No. 33, in whole or in part, at 100% of the principal amount being redeemed plus accrued and unpaid interest thereon to but excluding the Redemption Date.

For purposes hereof, the following defined terms shall have the meaning ascribed to them:

“Comparable Treasury Issue” means the United States Treasury security selected by an Independent Investment Banker as having a maturity comparable to the remaining term of the Securities of Series No. 33 (assuming, for this purpose, that the Securities of Series No. 33 matured on the Par Call Date) that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of comparable maturity to the remaining term of the Securities of Series No. 33.

“Comparable Treasury Price” means (i) the average of the Reference Treasury Dealer Quotations for the Redemption Date, after excluding the highest and lowest of such Reference Treasury Dealer Quotations for such Redemption Date, or (ii) if the Independent Investment Banker obtains fewer than four of such Reference Treasury Dealer Quotations for the Redemption Date, the average of all of the Reference Treasury Dealer Quotations for such Redemption Date.

4

“Independent Investment Banker” means one of the Reference Treasury Dealers appointed by the Trustee after consultation with the Company.

“Primary Treasury Dealer” means any primary U.S. Government securities dealer in the United States.

“Reference Treasury Dealer” means (1) each of BMO Capital Markets Corp., BNP Paribas Securities Corp., Credit Suisse Securities (USA) LLC and Scotia Capital (USA) Inc. (or their respective affiliates which are Primary Treasury Dealers) and any other Primary Treasury Dealer designated by, and not affiliated with BMO Capital Markets Corp., BNP Paribas Securities Corp., Credit Suisse Securities (USA) LLC and Scotia Capital (USA) Inc., or their respective affiliates or successors, provided, however, that if any of the foregoing or any of their respective designees, ceases to be a Primary Treasury Dealer, the Company will appoint another Primary Treasury Dealer as a substitute and (2) any other Primary Treasury Dealer selected by the Company after consultation with an Independent Investment Banker.

“Reference Treasury Dealer Quotations” means, for any Reference Treasury Dealer and any Redemption Date, the average, as determined by an Independent Investment Banker, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to an Independent Investment Banker by the Reference Treasury Dealer at 5:00 p.m., New York City time, on the third Business Day preceding the Redemption Date.

“Treasury Rate” means, for any Redemption Date, the rate per annum equal to the semiannual equivalent yield to maturity of the Comparable Treasury Issue, calculated using a price for the Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the Comparable Treasury Price for such Redemption Date. The Treasury Rate for any Redemption Date shall be calculated on the third Business Day preceding such Redemption Date.

The provisions of Sections 501, 502, 503, 504, 505 and 506 of the Original Indenture shall be applicable to the Securities of Series No. 33, except that (i) the notice of redemption required to be provided to Holders pursuant to Section 504 shall be provided not less than 10 nor more than 60 days prior to the Redemption Date and (ii) the notice of redemption to be provided by the Company to the Trustee pursuant to Section 502 shall be provided at least twenty-five (25) days prior to the Redemption Date (unless a shorter notice period shall be satisfactory to the Trustee).

(h) not applicable;

(i) the Securities of Series No. 33 shall be issuable only in denominations of $2,000 and integral multiples of $1,000 in excess thereof;

(j) not applicable;

(k) not applicable;

(l) not applicable;

(m) not applicable;

5

(n) not applicable;

(o) not applicable;

(p) not applicable;

(q) the Securities of Series No. 33 are to be initially registered in the name of Cede & Co., as nominee for The Depository Trust Company (the “Depositary”). Such Securities shall not be transferable or exchangeable, nor shall any purported transfer be registered, except as follows:

(i) such Securities may be transferred in whole, and appropriate registration of transfer effected, if such transfer is by such nominee to the Depositary, or by the Depositary to another nominee thereof, or by any nominee of the Depositary to any other nominee thereof, or by the Depositary or any nominee thereof to any successor securities depositary or any nominee thereof; and

(ii) such Securities may be exchanged for definitive Securities registered in the respective names of the beneficial holders thereof, and thereafter shall be transferable without restriction, if:

(A) the Depositary, or any successor securities depositary, shall have notified the Company and the Trustee that it is unwilling or unable to continue to act as securities depositary with respect to such Securities or the Depositary has ceased to be a clearing agency registered under the Securities Exchange Act of 1934, as amended, and the Trustee shall not have been notified by the Company within ninety (90) days of the identity of a successor securities depositary with respect to such Securities; or

(B) the Company shall have delivered to the Trustee a Company Order to the effect that such Securities shall be so exchangeable on and after a date specified therein; or

(C) (1) an Event of Default shall have occurred and be continuing, (2) the Trustee shall have given notice of such Event of Default pursuant to Section 1102 of the Original Indenture, and (3) there shall have been delivered to the Company and the Trustee an Opinion of Counsel to the effect that the interests of the beneficial owners of such Securities in respect thereof will be materially impaired unless such owners become Holders of definitive Securities;

(r) not applicable;

(s) no service charge shall be made for the registration of transfer or exchange of the Securities of Series No. 33; provided, however, that the Company may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection with the exchange or transfer;

(t) not applicable;

6

(ii) Notwithstanding the provisions of subparagraph (i) above, the Company shall not be required to give any notice specified in such subparagraph or to otherwise furnish any of the information contemplated therein if the Company shall have delivered to the Trustee an Opinion of Counsel to the effect that the Holders of such Securities will not recognize income, gain or loss for federal income tax purposes as a result of the satisfaction and discharge of the Company’s indebtedness in respect of such Securities and such Holders will be subject to federal income taxation on the same amounts and in the same manner and at the same times as if such satisfaction and discharge had not occurred.

(iii) Anything in this clause (u) to the contrary notwithstanding, the Company shall not be required to give any notice specified in subparagraph (i) or to otherwise furnish the information contemplated therein or to deliver any Opinion of Counsel contemplated by subparagraph (ii) if the Company shall have caused Securities of Series No. 33 to be deemed to have been paid for purposes of the Indenture, as provided in Section 901 of the Original Indenture, but shall not have effected the satisfaction and discharge of its indebtedness in respect of such Securities pursuant to such Section.

7

(v) The Securities of Series No. 33 shall be substantially in the form attached hereto as Exhibit A, and shall have such further terms as are set forth in such form.

ARTICLE TWO

Miscellaneous Provisions

This Supplemental Indenture No. 29 is a supplement to the Original Indenture. As previously supplemented and further supplemented by this Supplemental Indenture No. 29, the Original Indenture is in all respects ratified, approved and confirmed, and the Original Indenture, all previous supplements thereto and this Supplemental Indenture No. 29 shall together constitute one and the same instrument.

8

IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture No. 29 to be duly executed as of the day and year first above written.

The foregoing was acknowledged before me this 6^th day of March, 2019, by Sarah W. Soong, the Vice President and Treasurer of Public Service Company of Colorado, a corporation organized under the laws of Colorado, on behalf of the corporation.

Witness my hand and official seal.

My commission expires: January 31, 2020

[Signature Page – Supplemental Indenture (PSCo)]

On the 6^th day of March, 2019, before me personally came K. Wendy Kumar, to me known, who, being by me duly sworn, did depose and say that she is a Vice President of U.S. Bank National Association, the banking association described in and which executed the foregoing instrument; and that she signed her name thereto by authority of the Board of Directors of said banking association.

[Signature Page – Supplemental Indenture (Trustee)]

EXHIBIT A

FORM OF SECURITY

(See legend at the end of this Security for

restrictions on transfer)

PUBLIC SERVICE COMPANY OF COLORADO

First Mortgage Bond, Series No. 33

This Security is not a Discount Security

within the meaning of the within-mentioned Indenture