A connection-sensing DC plug has an insulative body, a connection portion, two power terminals, a conductive sheet and a retractable pin. The connecting portion is adapted to electronically connect to a target device and has an isolation layer and a ground layer. The conductive sheet is mounted in the insulative body and contacts either the isolation layer or the ground layer. The retractable pin is movably mounted in the insulative housing parallel to the connecting portion, with one end securely engaging the conductive sheet and the other end protruding from the insulative body. When the DC plug is connected to the target device, the retractable pin is pressed and moves inward to bend the conductive sheet, turning the conductive sheet to a floating state and resulting in a trigger signal.