See Electronics for Model Railways Book 1!
An adjustable 5v to 15v, 1 or 2 amp power supply.
This power supply has a very low output ripple and maintains a constant
voltage over a wide range of current.
The project can be used as a bench power supply or mounted along side other
circuitry on your layout. Extras needed:
Fuse and fuse holder
15v 2A transformer
1k linear Pot and knob.