A power supply including: a power supply circuit for receiving an external power and a battery power, and for outputting a power including at least one of the external power or the battery power to a load; and a battery pack coupled to the power supply circuit, the battery pack including a plurality of batteries, which are arranged into a plurality of battery groups including a first battery group and a second battery group, and configured to provide the battery power. Where, the battery pack is configured to selectively supply a power of the first battery group or a power of the second battery group as the battery power to the power supply circuit according to at least one of a status of the external power, a status of the load, a status of the first battery group, or a status of the second battery group.