Power converter circuitry and method

A switching power supply system comprising:

• a first switching power supply circuit having an input terminal for receiving an input voltage and providing a selected output at an output terminal;
• a second switching power supply circuit including a first input terminal connected to a first source of electrical potential, and having an output terminal coupled to the input terminal of the first switching power supply, for providing a voltage to the input terminal of the first switching power supply;
• a switching power supply controller having a first set of terminals coupled to the first switching power supply for providing control signals to the first switching power supply, a second set of terminals coupled to the first switching power supply for receiving information from the first switching power supply, a third set of terminals for providing control signals to the second switching power supply, and at least one terminal for receiving information from the second switching power supply, wherein the switching power supply controller is configured to provide one or more control signals to the second switching power supply to operate the second switching power supply in a first mode where the magnitude of the voltage provided by the first source of electrical potential is determined by the switching power supply controller to be sufficient to operate the first switching power supply to provide the selected output from the first switching power supply, and further wherein the switching power supply controller is configured to provide control signals to the second switching power supply to operate the second switching power supply in a second, different mode when the switching power supply controller determines that the magnitude of the first source of electrical potential is insufficient to operate the first switching power supply to provide the selected output.