There is provided a power supply unit supplying a standby power by sharing a switch of a main converter. The power supply unit includes: a main converter, and a standby converter. The main converter controls a current flowing in a primary side winding of a main transformer and supplies a main power through a secondary side winding of the main transformer. The standby converter controls a current flowing in a primary side winding of a standby transformer and supplies a standby power through a secondary side winding of the standby transformer, and a portion of a plurality of switches of the main converter is included in switches of the standby converter.