A power supply system includes a first circuit, a second circuit and a voltage controller. The first circuit includes a first power supply line connected to each of a first load, a power supply source, and a first battery. The second circuit includes a second power supply line connected to a second load and a second battery connected to the second power supply line. The voltage controller includes a DC-DC converter connected between the first power supply line and the second power supply line. The second load is able to perform a function that substitutes for at least part of a function that the first load performs. The voltage controller includes a converter control unit configured to control the DC-DC converter such that an output voltage higher than or equal to a voltage of the second battery is output to the second power supply line.