I had several old PC power supplies laying around the basement so I did some wiring and made a power supply for my lighted buildings.
It's a 230-watt AT power supply that should provide about 9 amps on the 12 volt drop. Being an AT supply (and not an ATX) it only provides -5v, -12v, +5v, and +12v...but I'm really only using the +12v so no problem. I had to wire a 10-ohm, 10-watt resistor in-line on the 5v line in order to get the full output on the +12v line. Since the resistor gets hot, I attached it to the grill on the back of the supply so the cooling fan blows air over it.
I attached a barrier strip to the power supply case and shortened the wires to keep the project self-contained. It was a little effort, and if I did it again I would just gather the similarly colored wires and terminate them on a barrier strip that was mounted nearby but not ON the supply.
Being an AT supply, it came with the power switch attached to an umbilical which I routed and mounted near my control panel. I screwed on a wire nut as a push button.
Considering a 100-watt model railroad transformer costs around $100 and I made this for free, I think I did ok.