Provided is a power source system that can more easily realize a configuration that can support a plurality of charging methods and supply a relatively high voltage and a relatively low voltage based on power from a battery. A power source system is a system that is to be installed in a vehicle including a travel motor, and into which a charging current flows via a charging path when receiving supply of power from an external apparatus provided external to the vehicle. The power source system includes a first conductive path and a second conductive path that are electrically connected to the charging path and branch from the charging path, a first relay that is provided on the first conductive path, and a first DC/DC converter that performs voltage conversion.