An out-door unit with multiple ports comprises a circuit block, a DC-DC converter and a plurality of ports. The DC-DC converter is configured to provide a first current to the circuit block. The plurality of ports is connected to a plurality of in-door units respectively via a diode and provides a second current from the plurality of in-door units to the DC-DC converter via a diode respectively. The circuit block requires an operation current, and a first part of the operation current is the first current from the DC-DC converter and a second part of the operation current is the second current from one of the ports.