Disclosed is an apparatus for supplying power to a device. The apparatus includes a transformer configured to output a predetermined voltage to a device varying in load; a switch configured to switch on and off the voltage output from the transformer in accordance with pulse width modulation (PWM) signals; a PWM signal supplier configured to supply the PWM signal to the switch; a feedback circuit which detects the output from the transformer and applies a control signal to the PWM signal supplier; and an output voltage controller which detects a load current of the device, and adjusts the control signal of the feedback circuit by adjusting the output detected by the feedback circuit in accordance with the detected load current.