POWER SUPPLY DEVICE

A power supply device includes: a high voltage power system including a high-voltage battery; a low voltage power system including a low-voltage battery of which an output voltage is lower than that of the high-voltage battery; a DCDC converter configured to step down an output voltage from the high-voltage battery and supply the stepped-down voltage to the low voltage power system; and a control unit configured to control a voltage to be supplied to the low voltage power system by the DCDC converter, based on a request from the low voltage power system and information representing a charge/discharge power of the high-voltage battery.