once more,
RV3 is to set the maximum current to 3 or 5 amps (one way to set: short the PSU, adjust P2 (amp) to max, adjust the RV3 to desired maximum current, be quick, the transistor will get HOT).
RV2 is to set the maximum voltage to 30v (how to set: in open circuit adjust the P1 (volts) to...