Power supply device and method that determine location of fault in first and second power supply systems

A determining method comprising:

• causing a determining unit of a power supply device including a first system configured to supply electric power of a first power supply to a first load, a second system configured to supply electric power of a second power supply to a second load, and an inter
• system switch configured to be able to connect and disconnect between the first system and the second system to keep the inter system switch in an ON state in a normal operation so that the electric power of the first power supply is supplied to both the first load and the second load, and in response to detecting a ground fault of the first system or the second system during the normal operation, turn OFF the inter system switch and determine, after the turning OFF, which of the first and second systems the ground fault has occurred in,
• after the turning OFF of the inter-system switch, causing a suppression circuit of the power supply device to simultaneously (i) suppress an electric discharge of the second power supply and (ii) supply electric power for ground fault detection to the second system, and
• after the turning OFF of the inter-system switch, causing the determining unit of the power supply device to determine whether or not any ground fault has occurred in the second system based on the electric power which is supplied from the suppression circuit to the second system.