in one embodiment , the invention is an apparatus having an isolated side and a line side . a line - side connector is connectable to a cable . an isolated - side physical - layer module is electrically coupled to the connector via a signal - isolation transformer and processes signals transmitted over the cable . a line - side power conditioning module is electrically coupled to an isolated - side power switcher via a power - isolation transformer that converts an ac power signal received from the power switcher into a transformed ac power signal and converts the transformed ac power signal into a cable power signal to be supplied via the connector to the cable in order to power a cable - powered device connected to the cable . an isolated - side control module performs a detection function in which the control module determines whether or not a cable - powered device is connected to the cable .