...Or buy a 12V DC-DC converter for your laptop.
I'm happy with my 5 years old investment:
http://www.intellesale.com/-item/20936/belkin-components-120w-universal.html?r161160Never tried the Airplane end though (probably, too shy to ask where is my personal power outlet in the plane

)
It had outlived all 4 of my older laptops. The original "bricks" are in dust on the far shelves.