An onboard power supply system for a motor vehicle includes a voltage converter and a voltage source which is electrically coupled with the voltage converter and is constructed for providing a predefined source voltage. The onboard power supply system further has a base energy accumulator which is electrically coupled with the voltage converter and is constructed for providing a predefined base voltage. With respect to the amount, the source voltage is greater than the base voltage. The onboard power supply system also has at least one first selection circuit of at least one first electric consuming device which can be electrically coupled parallel to the voltage converter. Furthermore, the onboard power supply system has at least one second selection circuit of at least one second electric consuming device which can be electrically coupled parallel to the base energy accumulator.