This circuit is a variable power supply using IC LR12 of Supertex inc. The difference of this circuit compare to variable PSU using LM317 is it can hold a high voltage input (100V) and can deliver an output of around 88V max down to 1.2V. This regulator is very suitable to DC circuits using higher voltage with current less than 100mA. The output voltage is controlled only by R1 and POT using the relationship below:
Voutput = 1.2(1 + POT/R1) + ADJ*POT or just use the LM317 calculator.
R1 - 560 ohms 1/4W
POT - 50 kilo ohms potentiometer
C1 - rated above 100V capacitor ( you can remove if DC is regulated)
C2 - 470nF (higher the better) capacitor rated 100V minimum
IC - LR12 or similar regulator IC
Note: The circuit is easy to construct but it is powered by high voltage DC that can be fatal. I dont recommend building this one if you don't have any idea in electronics. Remove only C1 if the DC input is regulated.
Read more at http://www.simple-electronics.com/2011/11/high-voltage-variable-power-supply.html#k63QU2qeqBJQ5pwG.99