A power switching circuit is provided, which automatically performs the necessary power switching, and by which the power specifications of external devices in a network can be uniformly determined. The power switching circuit comprises, for each external device, (i) a first diode for transmitting the power from the main device to the network, and for preventing power from reversely flowing from the network to the main device; (ii) a second diode for transmitting power from the external device to the main device, and for preventing power from reversely flowing from the main device to the external device; and (iii) a port for physically connecting the main device and the external device. The connection between the external devices is maintained regardless of the state of the power of the main device.