A power device includes a power supply module, a first electrical isolation unit, a second electrical isolation unit, a feedback control unit, and a comparing unit. The power supply module includes a feedback compensating terminal and an output terminal, the feedback compensating terminal provides a related voltage of output power, and the output terminal provides an output voltage. When the related voltage of output power is smaller than the predetermined voltage, the comparing unit controls the first electrical isolation unit to change operation of the feedback control unit and the second electrical isolation unit, to allow the power supply module to adjust the output voltage.