Another thing to consider is that typical quiet 80-120mm fans running off wall warts will only draw ~2-4 watts each (although I have a mean 120 that will eat 14 watts). If you use PC power supply it might draw a whole lot more than that even when it is only running 1 or 2 fans.
I have an old PC supply that I use for testing. I will dig out my Kill-A-Watt meter and run a couple quick tests. It will be interesting to see how the wall wort compares to the PC supply and the laptop supply.
My plain jane 2005 PC draws 175 watts even when it is just sitting there idling and that is not including the screen or anything fancy. My old 2002 laptop draws 35 watts including 15" TN LCD screen.