Seriously, every single department store, electronics store (Best Buy, Walmart, Target, etc.) and online sale site (eBay and a zillion importer sites) have cheap PSP chargers! The worldis not "out" of PSP chargers.
Seriously, buy a PSP charger. And undervoltage can do just as much damage as overvoltage, probably more. It's easy to clip input charging voltage in a device (and many do), but internal voltage boosting is not as common.