I was surprised to see that the PSP-2 can be powered by 5V, 500 mA which conforms to USB standard powering. I can't think of any other preamp in this size/performance category that has such minimal power requirements (Aerco, Sonosax, PSP-3, any others...?).
A while ago, I bought a slim USB battery pack for use with my iPod (APC UPB10). I hacked together a USB to DC jack (from an old AC adapter that I found to fit). Surprisingly, it powers the PSP-2 for quite a while, with Phantom 48V on. I recorded for 8 h, and the battery was only half drained. I'm sure there are smaller USB battery packs with more capacity nowadays since this is a pretty old battery.
Any other experiences out there with powering a PSP-2 with 5V? Any effect on sound quality or SPL handling?