To provide a power supply system for a vehicle which can appropriate charge a capacitor on a step-down side, and suppress system failure. The power supply system for a vehicle includes: a high-voltage battery; a first inverter which connects with the high-voltage battery; a drive motor which connects with the first inverter; a high-voltage DCDC converter which steps down the voltage of the high-voltage battery; an accessory, etc. which connects with the high-voltage DCDC converter; a capacitor which connects in parallel with the accessory, etc.; a current sensor, etc. which acquires the charging state of the capacitor; and a VCUECU which controls the high-voltage DCDC converter based on the acquired values of the current sensor, etc.