A power supply system comprises an alternating-current sweep unit that outputs alternating-current power from a U-phase battery string, a V-phase battery string, and a W-phase battery string that are Y-connected, a first power supply circuit that converts output of a direct-current sweep unit to alternating-current power using an inverter and outputs the alternating-current power, the direct-current sweep unit including a first battery string; and a control device. An energy density of a battery included in the U-phase battery string, the V-phase battery string, and the W-phase battery string is higher than an energy density of a battery included in the first battery string.