This patent specification describes a power adapter which includes a first amplifier configured to amplify a voltage difference between a voltage proportional to an output voltage of a switching regulator and a first reference voltage, a current detector configured to detect a current proportional to an output current of the switching regulator, a second amplifier configured to amplify an output signal from the current detector, a first converter configured to convert an output voltage of the first amplifier to a first current signal, a second converter configured to convert an output voltage of the second amplifier to a second current signal, an oscillator configured to oscillate with rectangular pulses and a controller configured to modulate an oscillation signal of the oscillator in accordance with the first and second current signals output from the first and second converters.