The circuit in Figure1 will give us 10 amps with performance that equals or exceeds any commercial unit. The circuit even has a current limiting feature which is a more reliable system than most commercial units have. This circuit uses the LM723 IC which gives us excellent voltage regulation. The circuit uses 3transistors 2n3055 which must be heat sinked. Potentiometer R9 allows the tuning of the voltage to 13.8 volts and the resistor network formed by resistors R4 ,R7 controls the current limiting.