An electrical supply device may include a transformer with a secondary winding to feed a current to a load; control circuitry for the device; an auxiliary supply source for said control circuitry. The auxiliary supply source may include an output capacitor across which a supply voltage is provided for said control circuitry; at least one charge accumulation capacitor to be traversed by the current fed to said load; a comparator sensitive to the voltage on said at least one charge accumulation capacitor; and a switch interposed between said at least one charge accumulation capacitor and said output capacitor, said switch coupled to said comparator, whereby when the voltage on said at least one charge accumulation capacitor reaches a reference level, said switch couples said at least one charge accumulation capacitor to said output capacitor by transferring onto said output capacitor the charge on said at least one charge accumulation capacitor.