A USB device and an operation method thereof are provided. The USB device includes a first switch, a second switch, a power converter, and a first USB connector. A first terminal of the first switch is configured to receive a first voltage. The power converter is configured to provide a second voltage, and the second voltage is less than the first voltage. A first terminal of the second switch is coupled to the power converter to receive the second voltage. A first power pin of the first USB connector is coupled to a second terminal of the first switch and a second terminal of the second switch.