This DC-DC Converter schematic diagram is very simple with few components, making it easy to build. It can convert 9 volt DC voltage from 12 VDC source.
To obtain a much more accurate output voltage, change zener Z1 using 10V and resistor R1 with a 1 Kohm Variable resistor. A heatsink for Q1 is recommended. Very simple circuit to be able to power your 9 volt electronic equipment and some other stuff.
R1 = 560 ohm
C1 = 1000µF/16V ( Electrolytic Capacitor )
C2 = 100µF/16 ( Electrolytic Capacitor )
C3 = 330nF ( Ceramic Capacitor )
Z1 = 9.1V, 0.4 watt ( zener diode )
Q1 = ECG184, NTE184