Power supply device and power supply system

The invention provides a power supply device and a power supply system capable of reducing the complexity of a circuit structure and reducing the component cost when a plurality of batteries are usedfor supplying power to electric equipment. The power supply device is configured such that: when voltage is output from an output unit using a plurality of battery packs connected to a plurality of (four or more) pack connection parts, on the basis of classifying the plurality of battery packs into any one of the first group of parallel connection parts and the second group of parallel connectionparts, the connection state of the first group of parallel connection parts and the output part is set to a fixed state, and the connection state of the second group of parallel connection parts and the output unit is switched. Such a configuration can reduce the number of connection state modes compared to a configuration in which the connection state between the plurality of battery packs (fouror more) and the output uni