This is a regulated and adjustable power supply which can deliver up to 20A and adjustable voltage between 4 and 30V. It is easy to build and uses LM338 and 741 integrated circuits. VR1 it is used to adjust the output voltage. Use very good heatsinks for LM338 and BD140 transistor. The transformer secondary must deliver 18 volts a.c.
Source: http://www.eleccircuit.com/high-power-supply-regulater-0-30v-20a-by-lm338/