POWER SUPPLY SYSTEM

A power supply system includes: a first power circuit having a first battery, a second power circuit having a second battery, a voltage converter which converter voltage between the first power circuit and second power circuit, a current sensor which acquires a passing current value Iact of the voltage converter, a passing power control unit which operates the voltage converter, and a failure determination unit which determines failure of the voltage converter. The failure determination unit determines that the voltage converter has failed in a case of the passing current value Iact becoming negative in a state in which the passing power control unit is not operating the high-arm element of the voltage converter to ON, and makes a time from when the passing current value Iact first became negative until determining that the voltage converter failed shorter as the passing current value Iact increases to the negative side.