Abstract: A power supply device is provided. The power supply device includes a power converter and a control circuit. The control circuit is coupled to a power converter. The power converter is configured to convert input power to provide output power. The control circuit is configured to receive a control signal and provide a dummy current according to the control signal and the output power, so that the sum of a current value of the dummy current and a current value of the output power is greater than or equal to a threshold value. The power converter can accordingly convert the input power in a soft switching manner.