A direct current backup power supply device of a data processing system with at least one computer supplied with very low voltage whose direct current power supply is connected to an alternating current power supply system using an AC/DC converter of alternating current into direct current includes means for storing electrical energy. The device also includes means for charging the means for storing electrical energy from a part of the direct current provided by the AC/DC converter to the very low voltage power supply of the data processing system, and means for discharging the stored energy in the means for storing electrical energy to the very low voltage power supply of the data processing system, to a noticeably constant predetermined very low voltage, following the detection of a micro-cut of the supply system.