You don't need a PSP charger to simultaneously charge and read. You can use a simple USB charger and use a PSP usb charging cable such as this one:
http://www.dealextreme.com/details.dx/sku.17983
It has a PSP compatible plug which gets connected to the power on USB port. The cable is pretty cheap on dealextreme (with free but super slow shipping), and I find it really convenient as I do not like to carry multiple power supplies when I travel, whether for my PSP or for my PRS 700.