Though 5 Volt is commonly used for microcontrollers, not seldomly higher voltages are required as well, such as 9 or 12 volt for relays or lamps.
The presented psu offers that and it came to life because i had an old 2×6 print transformer laying around that i finally decided to put to some use.
The rectification is a classic one to get a double voltage from 2 transformer coils, although one could of course use 2 bridge rectifiers. This gives a rough voltage of 8.5 and 17 Volt.
The rectified voltages are then stabilized to 5 and 12 volt respectively and we end up with 4 voltages as shown in the figure.
