I bought one of these from ThinkGeek: ThinkGeek :: Coffee Cup Power Inverter But I haven't used it yet. I see that the outlet on the Prius C has a 15 A fuse and they say not to use appliances that will draw more than 10 A (so 12 V at 10 W = 120 W). This device can deliver max 200 W continuous AC power (up to 400 W peak). So I guess this thing has the potential to blow a fuse. Am I probably okay as long as I don't draw too much power?
You could add an inline fuse holder and a 10 amp fuse. Lot 5X 3M Inline ATO/ATC Fuse-Holders 20A 18-14AWG #299 | eBay The manual says it expects to be on a 15 amp circuit http://www.originalpower.com/support/images/stories/manuals/0900-66,90309_Manual%28readers%29.pdf