A power supply apparatus requests the transmission of a requested PDO. A power receiving apparatus transmits the requested PDO in response to the request. The power supply apparatus modifies a first PDO list based on the requested PDO when it is possible to do so. The first PDO list is modified when the requested voltage is not defined in the first PDO list in a case in which a power supply circuit of the power supply apparatus is capable of supplying the request voltage indicated by the requested PDO. Subsequently, negotiation is performed based on the first PDO list thus modified.