In a PoE system, DC power is transmitted over two wire pairs. The primary winding of an isolation transformer is connected across the differential I/O terminals of a first PHY (a transceiver). A positive voltage output of a power supply is connected to a center tap of the secondary winding, and the secondary winding is coupled across a first wire pair. In this way, differential data and DC power is supplied to the first wire pair. A CMC is connected between the secondary winding and an autotransformer which is also connected across the first wire pair. A center tap of the autotransformer is also connected to the positive voltage output of the power supply, so that the current to the powered device is shared by the isolation transformer and the autotransformer. A similar circuit, with a second PHY, is used for the DC power return path.