This is a series of Power Supply. This adapter has an Output current of 12 volts and 20 Amperes ability. Power Supply Regulator circuit is normally used for a series that takes a large flow for example for radio transmitters, or for large Power Amplifier power and others.
The great streams of course for the use of power transistors in this case MJ 2955 requires a pretty good cooling, of course, with a fairly large Heatsink and finned and should also wear a cooling fan to the power transistor is not quickly broken.
Here the circuits:
good luck..