Abstract: A power supply has two energy sources, one of which has a relatively low energy density but provides a relatively high current and the other of which has a relatively high energy density but provides a relatively low current. One end of each of the energy sources is connected to an output terminal through a respective diode. The other ends of the energy sources are connected together to another output terminal. The power supply operates so that when the relatively low current is required by a load connected across the output terminals, the high energy density source provides the current; but when the relatively high current is required by the load, the current is provided from the low energy density source.