Switched power supplies are the modern and much more effective type of power supply. With them you can not only stabilize voltages without much heat loss, it is also possible to increase the input voltage almost arbitrarily.
This video shows and describes the function of step-up, step-down and buck-boost converters.

I refer to the following videos:
Voltage Multiplier:    • Spannungsvervielfacher, Villard Grein...  
Transistor power amps:    • Transistorverstärker Teil 3, Endstufe...  

0:00 - Introduction
1:32 - Step-Up Converter
4:05 - Pulse Width Modulator
5:40 - Step down converter
7:15 - Inverse converter