This DC power supply controller is controlled by pulse width modulation PWM, generated by the circuit around timer IC2 7555 according to the formula:
Duty cycle = ((R1 + (VR1/2)/(R1+R2+VR1)) x 100%
Diode D1 is used to bypass resistor R2 and half the effective resistance of the “lower” section of VR1, allowing the duty cycle to be [...]

This is the power supply circuit for general purpose usage.

The supply can be used for supply output voltages from 1 to 35V. The line transformer should be selected to give about 1.4 times the desired output voltage from the positif side of filted capacitor C1 to ground. Potensiometer R2 sets the output voltage to the [...]

You can use this power supply for your electronics project which only require electric current about 500mA. This is cheap circuit which will give you stabilized output voltage.
If you want to change the output voltage, you should change the IC type.
For example, you need 5V output, then change the IC from 7098 with 7805 dan [...]