In order to protect those subscribing to, purchasing or acquiring the notes, bonds, evidences of indebtedness or other obligations of the Public Service Authority, the State of South Carolina does hereby covenant and agree with any person, firm or corporation, the government of the United States of America, and any corporation or agency created, designated or established by the United States, subscribing to, purchasing or acquiring the notes, bonds, evidences of indebtedness or other obligations heretofore or hereafter issued or incurred by the Public Service Authority for any authorized purpose, that the State will not alter, limit or restrict the power of the Public Service Authority to, and the Authority shall, fix, establish, maintain and collect rents, tolls, rates and charges for the use of the facilities of or for the services rendered or for any commodities furnished by the Public Service Authority, at least sufficient to provide for payment of all expenses of the Public Service Authority, the conservation, maintenance and operation of its facilities and properties and the payment of the principal of and interest on its notes, bonds, evidences of indebtedness or other obligations, and to fulfill the terms and provisions of any agreements made with the purchasers or holders of any such notes, bonds, evidences of indebtedness or obligations heretofore or hereafter issued or incurred. Provided, however, that prior to putting into effect any increase in rates the Public Service Authority shall give at least sixty days’ notice of such increase to all customers who will be affected by the increase.