title was "High current PSU's and chargers using phone charger" caught by bug. When building linear PSU's or chargers getting a suitable transformer can be difficult/expensive. Some expensive units have transformers with an extra winding for powering the stabilser circuit or simply have 16v or more secondaries to overcome the dropout. (12v case) Today I just split open a switch mode, 4.9v phone charger and rescued a neat small pcb with an isolated output up to 500Ma. I'm thinking that if that was connected to add to the main rectified DC, it could supply an LM7812, which in turn feeds the multiple power (pass) transistors. The question then is would a 12v transformer suffice ? I'm assuming capacitors @ 2000uf per amp and a bridge rectifier - which reduces the drop out to 2v total off the main DC.