OK, it's a Targus Universal Auto/Air Power Adapter, model PA-350.
Input voltage: 11-16 Volts DC (sorry, not 24 as I saide before)
Output voltage: 3-24 Volts DC 8 Amps max.
Power: 70 Watts continuous
The aircraft end of the plug looks like this: (I'm not an artist
2 small prongs and 2 large prongs, protected by a hard plastic cylinder that extends half a centimeter beyond the ends of the prongs.
A cigarette lighter socket adapter is included, along with 6 or so laptop tips.
Hope this info helps.