I actually bought
this cable. The fun part is, that it has a normal USB port on one side an a mini-USB and a power plug on the other. I can use the same cable to update my PRS-300 and if I want to charge only I just use the other plug. I also had some cheap USB charger where this cable can plug in quite nicely. So, whether I want to charge (via USB or net) or want to synch, it is just one cable.
The price? I paid about €4 for it. The charger came with some other device, but can be picked up for €1-2 in some stores.
I really like this cable... PSP adapter are not that cheap here and p&p adds to much.