Abstract: The present invention is to provide a power supply device for a peripheral device, wherein a power input port of the power supply device is connected to a computer in order to supply power to a charging circuit of the power supply device for charging a rechargeable battery installed therein. When a power output port of the power supply device is connected to the peripheral device, the power supply device will enable an automatic switch assembly thereof to turn on a output switch and supply power from the computer to the peripheral device and enable the rechargeable battery to supply additional power to the peripheral device for compensating the inadequate power supplied by the computer and enabling the peripheral device to be operated in a normal condition.