A power supply device is provided. The power supply device includes a rectifier circuit for rectifying an inputted alternating current power supply, a capacitor circuit comprising a first and second capacitor which are connected in series, and smoothing the alternating current power supply rectified in the rectifier circuit, an inverter for converting the output power of the capacitor circuit to a preset power and outputting same, a switch for selectively connecting a middle node of the first capacitor and the second capacitor and an end of the alternating current power, a sensor for detecting a size of the alternating current power, and a controller which confirms a power mode of the alternating current power on the basis of an output value of the sensor, and which controls the switch so that the capacitor circuit multiplies and amplifies the selectively rectified alternating current power based on the confirmed power mode.