Ron - you are very welcome. If i remeber the Ohms law thingy, a pc power supply is roughly 200 watts? Power = current * voltage soooo , current = power / voltage, which in this instance 200watts / 12 volts = roughly 16.67 amps . That is a helluva lot of power for your trains. Remember if you want to do this, you will need a mini fused distribution center with the proper sized fuses and wire sizes. If you were to do this, split up your layout in several districts, limiting each district to now more than about 4 amperes . The actual train rail would prolly disintegrate at about 5 amps if a short were to occur, then accompanied by a fire on your layout - not good.....
Now all this districting is all im my head and not tested. I do not know if your DCC controller warrantee would be null and void if you used anything other than the prescribed power supply.
If it were possible and were to work, i will draw a distribution system for your districting for you... If you'd like ....... Like i said - a bit much power for your standard layout. Now a club where you were going to run about 20 - 30 choo choos, it would be more feasible.... I however am gullible and will build this system for my layout. Advantages = zero voltage drop. Disadvantages = if a short were to occur on your choo choo in an engine, the engine will disintegrate, instant flambe' ....
Soooo reconsidering this thing, id fuse each district to about 1 or 2 amps...