A power supply apparatus includes: a connection unit to which a battery pack is connected; a power conversion unit which converts direct current power output from the battery pack via the connection unit into a first power; a power plug which is connected to an external power source; a power supplying unit to which a power receiving unit of the external apparatus is connected to supply the first power output from the power conversion unit or a second power which is the power supplied from the external power source via the power plug; and a switching unit which switches between outputting the first power to the power supplying unit and outputting the second power to the power supplying unit.