I did some research into this many moons ago and compiled a good amount of information.
Clint Bradford wrote:
Personally, I would never run my laptop off a vehicle's charging system while the vehicle is running. You won't find many reputable laptop manufacturers recommending this.
I know for a fact that Dell, HP, and Acer all make car chargers. I consider them fairly reputable. :)
What kills laptops are adapters that don't "insulate" (for lack of a better word) the initial spike when you start your car. That can be fairly crazy on voltages and if the adapter passes that through, it can be fatal to computer equipment.
Tripp Lite PVINT375 (although this model comes with a cigarette lighter plug, that connection has to be one of the electrically most UNreliable for what we are doing - so the plug gets whacked off and the unit is wired directly) ... or
Astron Pi-250W 12VDC-to-120VAC inverter made for such circumstances. Wire it in to your vehicle's 12VDC system, and simply use your existing AC power supply. Immediate benefit is the ability to power/ charge other electronic items you may have using regular AC chargers.
While, yes, these will work, this is the most inefficient way of charging your laptop. Essentially you're getting AC from the alternator, converting it to DC for the car, converting it back to AC via the inverter, only to convert it back to DC to charge your laptop. Not good..