Abstract: An uninterruptible power supply system (UPS) includes a coupling choke (5) being operably arranged between an electrical load (2) and an external source of power (4). A generator (8) is operably connected to the coupling choke (5) on the side of the electrical load (2), and it is designed and arranged to be active during normal conditions and during trouble conditions. Trouble conditions are to be understood as conditions when the external source of power (4) fails. A converter (9) is operably connected to the coupling choke (5). A substitute storage device for electrical energy is operably connected to the coupling choke (5) on the side of the electrical load (2) by the converter (9). A fast-opening switch (6) is operably connected the coupling choke (5) on the side of the source of power (4), and it is designed and arranged to open in case of occurring trouble conditions.