Your laptop seems to draw a very high current, I guess most of the common laptop converters wouldn't deliver enough current.
My Toshiba laptop (Satellite L20-217) is rated at 3.42 Amps and 19 Volts. I use a dc-dc converter from the UK supplier Maplin (www.maplin.co.uk
) stock code L40BB. The input power lead is too short and connects to a cigarette lighter socket, I replaced the lead with a longer one rated for 20 Amps, and wrapped the lead through a large ferrite sleeve. To avoid setting the wrong voltage, I glued the selector switch and also glued the "power tip".
I've run both the laptop and my TS-480SAT "all day" on a 110 Ah leisure battery and both work happily together with no QRM from the laptop/psu.