Any thoughts on how the Samsung supplied cables are different? I have several USB cables of the same style, but only the cable that came with my SGP will actually charge the unit. It doesn't seem to be a voltage or current issue either because the factory cable will charge from an AC to USB power adapter or an automotive USB power adapter. But plug the physically compatible non-Sammy USB cable into the same adapters and the device doesn't charge. I have heard of folks having similar troubles with firmware upgrades using the USB cable to the PC.
Hang on to those original cables!