I just took delivery of a PSP data/charge usb cable from these people:

http://search.ebay.co.uk/search/search.dll...ntrypage=search

I wouldn't use it as my main charger, but for keeping the Z topped up at work and connected to USB it's perfect!

Disclaimer:
I am only connected to them as a satisfied customer and nothing else, and I make no warranties for your own experience.