Provided are a power supply device and a method of controlling the same. The power supply device includes: a power factor corrector which corrects a power factor of an initial power; a standby power supply unit which is connected to the power factor corrector, the standby power supply unit including a transformer which converts an input power received from the power factor corrector to a predetermined level of a standby power and comprises first and second coils; a sensor which is coupled to the second coil of the transformer and detects a level of an induced power corresponding to the input power; and a power supply controller which determines whether the level of the induced power exceeds a critical value when a system-on signal is received, activates the power factor corrector to correct the power factor of the initial power if the level of the induced power exceeds the critical value, and supplies a driving power to the system based on the level of the induced power detected after the power factor corrector is activated.