NOVELTY - The device has a control unit and an energy storage unit (19) comprising non-capacitive units having bias momentum wheels (20) or batteries (22). The non-capacitive units have a maximal admissible power and maximal deliverable power. The energy storage unit has supercapacitive units (24) comprising multiple series and/or parallel-connected supercapacitors. The non-capacitive units have a maximal admissible dynamic power and a maximal deliverable dynamic power.    USE - Used for supplying electric power to electricity consumers such as auxiliary equipments and electric motors embedded on a tractive unit (claimed) such as rail transit car, trolley-bus and electric motor bus that assures transport of travelers in suburban and urban areas.    ADVANTAGE - The device provides sufficient energy and power to supply the tractive unit on a distance separating several stations by using the bias momentum wheels, batteries or supercapacitive units while maintaining dynamic performances of the vehicle equivalent to that of the vehicle supplied with a traditional system such as catenary or current rail or heat engine. The device reduces installation expenses and avoids breakdown of catenary or an electric problem on a portion of the supply rail while eliminating blockage of the rail traffic. The device provides enough power to maintain a sufficient speed of the vehicle and to carry out a displacement on the distance separating several stations. The supercapacitive assembly that is able to deliver strong powers is compact and has a low mass, so that it is easily fixed on the roof of the vehicle.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (A) a method to supply power to electricity consumers such as auxiliary equipments and electric motors embedded on a tractive unit    (B) an information medium comprising a computer program having instructions for executing a method to supply power to electricity consumers.    DESCRIPTION OF DRAWING(S) - The drawing shows an electrical diagram of a power circuit of electric power supply device.    Power supply device (2)    Energy storage unit (19)    Bias momentum wheel systems (20)    Power batteries (22)    Supercapacitive units (24)