This useful power supply can provide voltages from 0 to 12 V with currents up to 2 A, set in potentiometer P1. The transistor must be provided with a good heat radiator and the zener diode is 12V6 with 1W dissipation. The secondary winding of the transformer can be 12 + 12 V or 15-15 V with a current of 2 A. The output voltage indicator is optional, since in its place we can use the multimeter. The circuit does not have short-circuit protection at the output. Filtration can be improved by increasing capacitor C1 to 2 200 uF or even 4 700 uF. The working voltage of this component must be at least 25 V.