The PurePower is an awesome little unit. It feels really substantial and durable with a great chassis and nice fit and finish. It is a notable step up from the AQVOX low-noise linear usb power supply (which was in itself a nice improvement over AP2 stock). Coming straight from the AP1/2 to the PurePower would seem like an awesome improvement without having had the Aqvox in between.
The additional improvements are similar to those the AQVOX brought, only better. I am getting a very black background, effortless low level detail, and an organic/musical touch that adds much more of an immersive experience to my ears. Compared to my setup sounding awful while the AP2 was away getting modded, it sounds glorious right now.
I'll have to post my AQVOX in the for sale forums tomorrow and save some lucky chap an arm and a leg in shipping from Germany. It cost me $75 to ship the dumb thing from Germany this last Christmas :0.