Power supply device and method for portable electronic device

The invention discloses a power supply device and a power supply method for a portable electronic device. The power supply device comprises an external power connector, a battery, a first converter set, a second converter set and a switching network. A power input end of the first converter set is coupled to the external power connector, wherein the first and second converter sets provide operating power required by the portable electronic device. When the operating power of a system is smaller than the preset power (such as adapter power), the switching network couples the second converter set to the external power connector, and the system is powered by an external power supply; and when the operating power of the system is greater than the preset power, the switching network couples the second converter set to the battery, and one part of power supply is provided by the external power supply and the other part of power supply is provided by the battery. Therefore, an adaptor with small power can be selecte