REDUNDANT POWER SUPPLY SYSTEM

A redundant power supply system comprising: a sub power supply; a first circuit; a second circuit for supplying power of the sub power supply to the plurality of loads; and a control unit for controlling operations of the first circuit and the second circuit based on a state of the main power supply, wherein the control unit operates only the first circuit when there is no failure notification of the main power supply from the plurality of loads, and when there is no failure notification of the main power supply from the first load, and when there is a failure notification of the main power supply from the second load, which is one of the plurality of loads, operates only the second circuit, and then operates the first circuit when the voltage of the sub power supply decreases to a predetermined lower limit voltage.