In a power supply apparatus, an upper-arm control unit includes a first switching element connected between a DC power source and a primary side of each upper-arm transformer. The upper-arm control unit controls on and off operations of a first voltage-controlled switching element to control supply of an output voltage of the DC power source to the primary side of each upper-arm transformer. A lower-arm control unit includes a second voltage-controlled switching element connected between the DC power source and a primary side of the at least one lower-arm transformer. The lower-arm control unit controls on and off operations of a second switching element to control supply of the output voltage to the primary side of the at least one lower-arm transformers. Each upper-arm transformer is arranged adjacent to the upper-arm control unit, and the at least one lower-arm transformer is arranged adjacent to the lower-arm control unit.