Mechanical voltage regulator for laboratory power supply?

Question

Power Supply

Good afternoon! I am new to electronics and circuitry, which was the reason for writing this text.
The essence of the question is this: there is a laboratory transformer power supply. The transformer takes 220v and gives out from 0-20 (19.8, as I understand it, 0.2 scatter according to the resistance of the wires and power supply elements)
According to my observations, there are two large capacitors in the power supply circuit, a rheostat, an LED for indicating on / off and a toggle switch.
The rheostat was broken and the idea arose to make a human laboratory power supply for myself, as they say.
I want to connect A and B meters and replace the rheostat with a set of toggle switches that will give me a stable voltage of 3.3; 5; 12 in
QUESTION: how to implement a voltage regulator?! Toestd how to make it so that including one toggle switch I get 3.3v including another 5v, 12v and so on. In this case, the voltage should be kept regardless of what load I connect.
They told me about some kind of rolls and other things, but nothing went to pieces in my head.
Please help!!!))

Answer 1

Read the basics , maybe it will clear up