If the fan has a molex connector, its probably a 12v fan. The one you mentioned with the 3 wire is a 12v fan--it should say it on the fan... something along the line of "DC12V .15A". One positive, negative, and rpm control. I've used those fans before for my light fixture. I cut the rpm control wire since its not needed. I used an old 12v wall adapter (typically from old cable modem, router, cd player charger, etc) then connect the 2 fan wire to the adapter wire... and wala.
FYI, I used 2 120mm (one on each side) PC fan hooked up to a 12v wall adapter for my lighting fan. Its much cheaper than buying 2 120mm 110v fans. My 3x250mh + 2x96pc fixture is always cool. Just make sure the amperage rating of the adapter exceeds the output of the fan(s).