The mission of the regulator-rectifier is to generate direct current to power all electrical equipment on board.
To this end receives alternating current generated by the alternator coupled to the motor. The current generated by the alternator varies in frequency and amplitude as a function of engine rpm.
The regulator-rectifier must be capable of maintaining a continuous voltage output of about 13.8 V regardless of engine rpm and the loads connected to it.
1st generation regulators (or linear) dissipate as heat energy generated in excess of 13.8 V that is not consumed by the loads.
2nd generation regulators (or switching) are much more efficient as they are able to "get" just enough energy to avoid dissipating excess.