Abstract: A power supply device communicable with a system and a method for supplying power to a system through a switch thereof are disclosed. The power supply device includes a switch, a microcontroller unit and a control circuit, and supplies power to the system through the switch. The microcontroller unit provides a first operating voltage to the switch through a first pin, and performs a firmware update procedure when the power supply device communicates with the system. The control circuit is coupled to the switch, and transmits a second operating voltage to the switch. When the microcontroller unit performs the firmware update procedure, the control circuit turns on the switch at least according to the second operating voltage, so that the power supply device does not stop supplying power to the system.