Abstract: A power supply for both alternating current (AC) and direct current (DC) which has an AC/DC converter and DC/DC converter detachably coupled with each other. The AC/DC converter is adapted to convert an AC input voltage into a DC signal, and the DC/DC converter is adapted to convert a DC input voltage into a DC signal. An output voltage selector is provided to obtain a DC output voltage appropriate to an associated device. The present power supply can be conveniently carried, supply power to an associated device regardless of AC and DC input voltages and select a level of an output DC voltage. Therefore, the present power supply can be used universally irrespective of the types of associated devices and manufacturers.