This chapter applies to contracts for the procurement of supplies, services, and construction, entered into by the City after August 1, 1991, unless the parties agree to its application to contracts entered into prior to the effective date. It shall apply to every expenditure of public funds by a public agency for public purchasing, irrespective of the source of the funds. When the procurement involves the expenditure of federal assistance or contract funds, the procurement shall be conducted in accordance with any mandatory applicable federal law and regulations. Nothing in this chapter shall prevent any public agency from complying with the terms and conditions of any grant, gift, or bequest that is otherwise consistent with law.