The French-German Research Institute of Saint-Louis obtained essential parts of a 30 MJ energy supply formerly installed at Rheinmetall in Unterlus, Germany. This paper describes the original state of the energy supply, the refurbishment of one rack with a stored energy of 1.28 MJ and its testing, taking into account worst-case conditions. The rack was split into two subunits of 675 kJ and 608 kJ which were upgraded with newly developed high-power thyristor and crowbar diode assemblies. The subunits were successfully tested individually and in the pulse shaping mode by connecting them to a common load. Several tests with voltages up to 22 kV, currents up to 267 kA and a different trigger delay proved the reliability of the modified rack and its suitability as a prototype for the remaining 23 racks.