VEHICLE POWER SUPPLY DEVICE

A power conversion unit includes an AC/DC converter converting alternating-current power supplied from an AC power supply into direct-current power to charge a high-voltage battery with the direct-current power and a step-down DC/DC converter generating an intermediate voltage provided by stepping down a voltage of direct-current power supplied from the high-voltage battery. A constant-voltage DC/DC converter outputs, to a low-voltage load unit, direct-current power provided by stepping down the intermediate voltage of direct-current power output from the step-down DC/DC converter at a constant step-down ratio.