POWER SUPPLY DEVICE AND POWER SUPPLY SYSTEM

A power supply device may include a body case, a first device-side engaging part disposed on the body case, a first output part disposed on the body case; and a device-side connector configured to be connected with a battery-side connector of a first battery unit. The body case may include a bottom surface, and an upper surface configured to allow the first battery unit to be placed thereon. The first device-side engaging part may be configured to be engaged with a first engaged part of the first battery unit. The first output part may be configured to output power supplied from the first battery unit to a first external apparatus different from the first battery unit.