I've repurposed a laptop-style 12V @ 3.3A supply and it only works some of the time.
If you are going to use a heated print bed, the general guideline is 20 amps at 12V. 30A is better. Without a heated bed I think you need a minimum of 6A.
You can get 12V 30A supplies from ebay for about $35. Very easy to wire up, and lots of headroom.