You have a couple of choices. Lind makes adapters for most Dell laptops.
Second choice is a Radio Shack power adapter with selectable voltages
from about 6v to about 21v (good for many different devices), but only
about 30w, and interchangeable tips.

Do check up on AA's seat power (I'm a United fan) and make sure
that they are 12V Car - there's the EMpower system that's also
12v. For the above mentioned adapters there are EMpower to Car
adapters.

If the power draws are not compatible then a portable battery
power pack may do it for you.

Bob