A power supply comprising: an inputter including an input capacitor and configured to receive an input DC voltage; a converter including an inductor and an output capacitor and configured to convert the input DC voltage and output the converted DC voltage, the converter further comprising a first switch and a second switch; and a controller configured to control the converter to output a voltage corresponding to a reference voltage, wherein in response to the reference voltage being changed, the controller is configured to control the converter to provide a charge stored in the output capacitor to the input capacitor based on the changed reference voltage, wherein the controller comprises a variable voltage driving circuit configured to generate a current offset for changing a direction of current flowing through the inductor, and adjust the reference voltage, wherein the controller further comprises a current detector adapted to detect actual inductor current, characterized in that the controller further comprises: means to add the current offset to the detected actual inductor current to form a detection value larger than the actual inductor current value, and a pulse width modulation, PWM, signal generator configured to generate PWM signals (131-1, 131-2) for alternately controlling the first and the second switches (121, 122) based on the detection value, the detected output capacitor voltage and the changed voltage reference. an inputter including an input capacitor and configured to receive an input DC voltage; a converter including an inductor and an output capacitor and configured to convert the input DC voltage and output the converted DC voltage, the converter further comprising a first switch and a second switch; and a controller configured to control the converter to output a voltage corresponding to a reference voltage, wherein in response to the reference voltage being changed, the controller is configured to control the converter to provide a charge stored in the output capacitor to the input capacitor based on the changed reference voltage, wherein the controller comprises a variable voltage driving circuit configured to generate a current offset for changing a direction of current flowing through the inductor, and adjust the reference voltage, wherein the controller further comprises a current detector adapted to detect actual inductor current, characterized in that the controller further comprises: means to add the current offset to the detected actual inductor current to form a detection value larger than the actual inductor current value, and a pulse width modulation, PWM, signal generator configured to generate PWM signals (131-1, 131-2) for alternately controlling the first and the second switches (121, 122) based on the detection value, the detected output capacitor voltage and the changed voltage reference. means to add the current offset to the detected actual inductor current to form a detection value larger than the actual inductor current value, and a pulse width modulation, PWM, signal generator configured to generate PWM signals (131-1, 131-2) for alternately controlling the first and the second switches (121, 122) based on the detection value, the detected output capacitor voltage and the changed voltage reference.