Abstract: The invention relates to a power supply device, particularly for a motor vehicle, with an internal combustion vehicle engine (FM), actuating a first rotary current generator (DG1) and a internal combustion supply engine (VM), actuating a second rotary current generator (DG2), whereby a controlled alteration switch (BS) connects the rotary current generator (DG1, DG2), which is currently in operation, to a first voltage converter (K1), topping a secondary converter (K2), the output voltage (UB) of which feeds low-voltage consumers (V) and an accumulator battery (AB), characterized in that the first voltage converter (K1) is a direct-voltage generator with solid-state circuit elements (MOS), which is polyphase high-frequency pulse-length regulated, generating an intermediate direct voltage (UG), which is converted to the low output voltage (UB) by the second voltage converter (K2), a direct-voltage regulator with a solid-state circuit element (MOS1), which is high-frequency pulse-length regulated.