An electronic device includes a case containing a universal serial bus (USB) transmission port, an embedded control unit, a central processing unit, a power supply unit and a multiplex control unit. The multiplex control unit has a first usage mode and a second usage mode. The multiplex control unit is normally in the first usage mode, and switches to the second usage mode when a switch signal is received. In the first usage mode, the multiplex control unit is powered by the power supply unit, and the multiplex control unit builds up a first transmission path between the central control unit and the USB transmission port. In the second usage mode, the multiplex control unit is powered by an external device connected to the USB transmission port, and the multiplex control unit builds up a second transmission path between the embedded control unit and the USB transmission port.