While Nice, I've had limited success charging my PSR-500 of the USB (Not sure about the 505 as I don't have one), and not wanting to carry another charger 'Brick' around, I decided and got a retractable cable which I could use both for Transferring files and Charging.
So I got the
Logic3 Data And Charge Cable (PSP)
I've had it for over a year, and its worked great, as I've also used it to power a number of other gadgets such as my Archos Player (Slowly, in an emergency) and a Portable Speaker.