You can get high-quality stable 12 v from a PC power supply. THere is just a small trick to turn on the PS withouth a board. Warning you may not be able to use your PS to power your computer after that because of damage to internal circuitry.
I wrote a post about this a long time ago:
http://www.lebgeeks.com/forums/t3734-Power-with-power-supply.html
I think it will give you more then 1000 mA. If not then you can wire 2 or more in parallel.
Max amp load is usually written for each voltage on a stickers on the power supply. You can also convert watts to amperes, but dont ask me the formula.
