Help Droid Powers off when USB is in use


When i plug the USB in I have to be sure that I'm perfectly still. If the phone moves at all it Reboots. It is the factory USB charger that came with phone? Any suggestions? Is it just faulty cable or should I go through the trouble of getting a new unit?
Mine is doing this now too. I haven't used the USB cable in a week or so and I usually only use it to charge -- most of my file transfers are ftp over wifi. But today when I plugged in the stock USB cable I rebooted. I tried plugging it into the phone first, then computer.. and computer first then phone.. rebooted over and over until I unplugged it. I'd sure like to know why and what to do about it.