A power adapter comprises a main power circuit, a feedback circuit, an ID detection circuit and a switch controller. The feedback circuit is coupled to the main power circuit for detecting the DC output voltage and issuing a feedback signal. The ID detection circuit is coupled to the feedback circuit for detecting an ID signal from the DC-powered electronic device and issuing a control signal to the feedback circuit to disable or delay the feedback signal for a specific time period, and comparing a dropping slew rate of the DC output voltage with a preset value to issue a hiccup mode control signal. The switch controller is configured for controlling the operations of the main power circuit in response to the feedback signal and controlling the power adapter to operate in a normal operation mode or a hiccup mode in response to the hiccup mode control signal.