I have used the cigarette lighter powered 400W models for over 20 years for various computer and phone charger applications. HOWEVER, during a 11 day winter power outage I was powering a 19" 3 speed box fan (to blow heat off the wood stove) after about 45 minutes it blew the fuse as expected when I checked the fuse it was good, the cigarette lighter itself was dead! That was a 1999 S-10.
2 fall seasons ago I had a short term job that involved alot of down time. It had turned unseasonably cold so I sat in the truck 45 min of the hour in the mid-day and spent quality time on the Smith & Wesson Forum. My lap-top battery has no storage capacity anymore so it was pretty much a direct drive/charge situation with a converter not much bigger than my wallet. This converter stays in my laptop case all the time now.
Back in the late 70's I had a 1000 W converter that worked very well, SORT OF! It took 12 V DC direct from the alternator and converted it to 110 V DC not AC. Some of my power tool were 110 or 120 volt AC/DC so it was fine and saved me from lugging a gas powered generator around for small jobs on the farm, but not really a back up energy source. It would run a 7 1/2 inch circular saw and 2" roto hammer, and they draw pretty high amps! Ivan