Abstract: A heavy duty converter including case and cover elements defining a case and cover assembly and a transformer subassembly with or without rectification within the case and cover assembly wherein flange and pin means are provided on the case and cover elements for coacting with the transformer subassembly to resiliently support the subassembly and to maintain the transformer subassembly in spaced relation to the walls of the case and cover assembly such that the hot spots of the transformer subassembly are so located as to allow efficient dissipation of the heat. Where plug-in terminals are provided for input to the power pack, the terminals are secured in place to the cover of the case and cover assembly. Various output rated transformer subassemblies may be used in the same case and cover assembly wherein the bobbin for each given size of transformer subassembly will include identical outer flanges for coaction with the flanges and pins on the case and cover assembly.