The Magellan GPS car charger I got from Magellan 800 860 2000 2200T GPS AC Car Charger 980827 - eBay (item 380205207395 end time Apr-04-11 20:13:49 PDT) works. The plug is a perfect fit for the S7, and the output is listed at 5V 2A.
The one I got is within $10 shipped.