A power supply device includes a battery, a charging part charging the battery, a power input to receive adapter power from an adapter supplied with external power or power output from a similarly configured power supply device, a power output part to output the adapter power, the power output of a similarly configured power supply device, or the battery power of the battery, and a controller to control the input power to apply power to the charging part and the power output part when the input power is supplied to the power input part, and to control the battery to apply power to the power output part when the input power is not supplied to the power input part. Thus, the power supply device is capable of applying power from an adapter to a portable electronic device while charging an internal battery with the adapter power.