This is a low-cost adjustable power supply unit which is capable of supplying up to 20A to any load. The circuit is based on LM338 adjustable linear regulator which is capable of supplying in excess of 5A over a 1.2V to 32V output range. Using 4 x LM338s, we have a powerful 20A adjustable power supply unit. The electronic circuit is very simple and also scalable.
You can build it even without a PCB. Just mount the regulators on a large heat-sink and place it inside a box. Solder the resistors directly on the regulators and place everything else in the same box. Make all the connections using cables of at least 2.5mm in diameter. Probably, you will also need a good air blower. Remember, this is a linear regulator and a lot of power is wasted on heat. Heat losses greatly increase if the output voltage is adjusted to be much less than the regulators input voltage. Choosing the transformer's output voltage to be close to the required output voltage is the best way to avoid losses.