POWER SUPPLY DEVICE AND CONTROL METHOD

A power supply device includes: a first system connected to a first load; a second system connected to a second load; an inter-system switch configured to connect and disconnect the first system and the second system to and from each other; a controller configured to normally supply power of a first power supply to the first system and the second system and, in response to a fault of the first system being detected, turn off the inter-system switch to supply power of a second power supply to the second system; and a backup circuit which includes a discharge regulation unit configured to regulate discharging of the second power supply.