Thermaltake makes some good 2u cooling solutions. Power supplies are a large generator of heat. They are taking 110/115 volts and turning it into 500-700 watts on a typical gaming machine. Based on the average efficiency of the cheap psus that most people use, I’d say that’s one of the larger heat producers. Then it takes a huge fan and blows all that heat right into a room. Kip pretty much summed the rest of it up.