A power supply apparatus includes a main body, a power input device, a first power output device and a second power output device. The first power output device includes a first cable and a first connector. The first cable is connected to a first surface of the first connector and includes at least a stop block and at least a fastening element. The second power output device includes a second cable and a second connector. The second cable is connected to a first surface of the second connector and includes an extension part and a retaining wall. An edge of the retaining wall is confined by the stop block and the extension part is clamped by the fastening element so as to selectively combine the first connector with the second connector as a composite connector assembly and facilitate securely fixing the composite connector assembly in a common power socket.