this is a fixed voltage power supply, in this power supply we use certain components:-
1) Transformer (12 volts)
2) Bridge Rectifier
3) Voltage Regulator (7805 for 5 volt supply, 7809 for 9 volt supply)
4) Capacitor as shown in circuit diagram
5) Diode (D5 IN4007)
In this voltage regulator regulates the power supply to such a extent which is required in the project, so you can use 7805 for preparing 5 volt supply and for 9 volt supply you use 7809.