Radio Shack has one with multiple adapter tips for different types of applications, gps, cell phone, palm, etc. but the guy wanted to know what the power requirements are so I don't pick a cord the fries the gps unit? do I have to be concerned about that in any cord that I pick?
I'm not sure why you're fooling around with Radio Shack. I'm not aware of any Rat Shak cable that would have a USB adapter tip. Even if they make one, you run the risk of plugging the tip in backwards, thus reversing polarity and trashing your GPS. Plus, you'll spend $15-20 on the plug & adapters.
Just get a generic USB cell phone adapter at Walmart, Target, Rat Shak, etc. Power requirements for the GPS are minimal, probably less than 100 ma, certainly less than any cellphone's requirements. You shouldn't have to spend more than $10. Otherwise, just buy a Garmin adapter.