You need regulated 5V. 2A will probably be enough unless you have ZIP
(which takes a lot on spinup) or hard drive (ditto). We used some 5V@4A
supplies for a while before finding the larger but less expensive 6A
ones that shipped. You should be ok with anything that meets that spec,
I don't have a digikey catalog handy, but it wouldn't surpries me if
they have something. Just make sure its regulated and the plug polarity
is correct. 

Mark