From:

https://circuitsstream.blogspot.com/2016/03/simple-138v-and-20a-dc-power-supply.html

This is the Simple 13.8V and 20A DC Power Supply Circuit Diagram.

The circuit was designed to create a DC power supply that will be rated with 13.8 V and 20 A while having a current limiter and short circuit protection. 

Components

7812

7812 Voltage regulator is a type of self-contained fixed linear voltage regulator integrated circuit. The IC belongs to ic 78xx voltage regulator family.

The 7812 voltage regulator IC is ease-of-use and available in very low cost. The last two digits of 7812 indicates the output voltage that is 12 V

7812 voltage regulator

BUZ11

N-Channel Power MOSFET 50V, 30A, 40 mΩ This is an N-Channel enhancement mode silicon gate power field effect transistor designed for applications such as switching regulators, switching converters, motor drivers, relay drivers and drivers for high power bipolar switching transistors requiring high speed and low gate drive power. This type can be operated directly from integrated circuits.

References