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 .