QUOTE What are th pros & cons of using a computer power supply? I was recently given one rated at 12v/15 amps.
John, first of all, this won't provide the power you need for cars like group 20s. For each car like that, figure on a supply that can output at least 5-8 amps per lane. Mine puts out 6 and can barely handle them, and chokes on anything hotter - okay because I don't run even those anyway! Not only is the computer supply underrated, but they have another drawback. Unless it is an old unit, it will be a switch-mode supply. Most switching supplies do not work properly in the slot car environment because they are designed to work with a constant load of some level - they don't react well when confronted with no-load situations and full-load situations when the load is also inductive (as with slot cars).
QUOTE The other alternative i'm considering is a car battery and trickle charging.
If you don't have access to a suitable electronic supply, this is the best alternative. Personally, I don't like batteries, and have justified reservations about them, but they can often be the most affordable and effective power source when you get into high-amp cars as you are. Just take all the right precautions if the batteries will be stored indoors. And look after them religiously.