A power supply capable of protecting a rectifier circuit using a switching element from an overvoltage or an overcurrent is provided. The power supply includes a power input terminal; an output capacitor; a synchronous rectifier configured to rectify an AC voltage input through the power input terminal; a converter configured to convert the rectified AC voltage into a DC voltage following a preset voltage and supply the DC voltage to the output capacitor; and a protection circuit provided between the power input terminal and the output capacitor, and configured to supply an AC voltage higher than the voltage charged in the output capacitor to the output capacitor by bypassing the synchronous rectifier.