A control system for a vehicle power supply for supplying power to a predetermined power receiving portion includes a first power generating power supply portion, second power generating power supply portion, and controller. The controller is arranged to set the voltage to be output to the power receiving portion from one of the power generating power supply portions in accordance with the output voltage of the other of the power generating power supply portions. With this arrangement, the power receiving portion is prevented from being supplied with an excessive amount of power, and when power regeneration is being performed by the second power generating power supply portion, the regenerated power is effectively used. Thus, the fuel economy of the vehicle can be increased.