A power supply apparatus supports USB-PD (Universal Serial Bus-Power Delivery) specification. A bus voltage VBUS is transmitted via a bus line. A first power supply circuit generates a first bus voltage having a first voltage level. A second power supply circuit generates a second bus voltage having a second voltage level that is higher than the first voltage level. A first switch is arranged between the bus line and an output terminal of the first power supply circuit. A second switch is arranged between the bus line and an output terminal of the second power supply circuit. A control circuit receives a control signal S1 via the bus line from a power receiving apparatus, which is a power supply target. The control circuit is structured to control the first switch and the second switch based on the control signal S1.