A power supply device is disclosed. A circuit board is disposed inside a conductive housing. A rectifying module is disposed on the circuit board and has primary and secondary sides. The grounding module includes a first grounding element, a second grounding element, and a fastening element. Two terminals of the first surge protection module are respectively electrically connected to the primary side and the first grounding element. Two terminals of the second surge protection module are respectively electrically connected to the secondary side and the second grounding element. The second grounding element and the first grounding element are not directly connected. The fastening element passes through the conductive housing, the circuit board, the first grounding element, and the second grounding element so that the conductive housing, the first grounding element, and the second grounding element are electrically connected to one another.