I looked into one made by Targus. It said it would only power the laptop in power saving mode and wouldn't charge it.

I found one by Lind Elec. that provides full power and charges, but it costs more than the 150w pure-sine inverter I found. I would rather have an inverter because it has more uses, even if I don't have more at the moment. At the least, the inverter should work on future laptops, which the adapter probably wouldn't.