Easy Qn first.
What are the differences Between the PW120 and the PW200? I can only see the different size/shapes.

Now. The ITPS, How can you run that with the likes of the PW120? I mean, the PW120 is supposed to put out 200W, but the only voltage reg in the ITPS is putting 5A out (@12v - 60W). Something doesnt quite add up there :S

Now, looking at the PW120, am I correct in assuming that it regulates all other voltages apart from 12V?

So to get the best sorta power out of it, why not regulate the 12V line after the PSU?