something like this should work with any 5V charger that charges via usb.
http://www.amazon.com/3-5mm-Barrel-J.../dp/B00512Z86I
or get a generic psp charger like this:
http://www.amazon.com/PSP-AC-Adapter-Sony/dp/B0007U2CX6
if you want the assurance of the genuine thing but at a much higher cost:
http://www.amazon.com/PSP-AC-Adaptor...ny+psp+charger
it's surprising that item 2 is actually less expensive than item 1.