A power source system includes a first power source, a second power source, a Direct Current to Direct Current converter, a first load including a vehicle control device configured to perform predetermined control regarding at least one of traveling, steering, and braking of the vehicle regardless of a driving operation performed by a driver of the vehicle, and an electric actuator as a control target of the vehicle control device, and connected to the first path so as to be supplied with power from the first power source, and a power source control device configured to control an operation of the Direct Current to Direct Current converter such that power is supplied to the first path from the second power source in a case where the predetermined control is performed.