I have a Kensington 70 Watt power adapter that I use both aboard and in my minivan to power my Dell D610 and my Dell ATG.
(similar Kensington unit)
The removable Tips are unwieldy, but I think it's more efficient than using an inverter and AC/DC adapter. I must have the tip that only powers, but does not charge, the computer.
I am considering adding a couple of storage batteries in a space near compression post on my Ranger 33 as a second bank to dedicate exclusively to ships computers. When I have my cell phone and PC and anchor someplace with a strong Sprint PCS signal (Fort Townsend State Park has five bars of signal at the mooring buoys !) it's just like I'm at the office. Except I'm smiling every morning.