Yes that's right but how much current does the car adaptor need to deliver? eg What does the display require?
The part number for the mains adaptor he has hints that it might be rated for 6A (eg 30W). The car adaptor suggested above is rated for only 2.1A (10.5W).
Edit:
Finding a 12V to 5V 30w car adaptor off the shelf isn't easy (at least I couldn't google one) Most car adaptors of that power rating are for laptops and produce 15V rather than 5V.
If the display needs 6A (30W) and you can't find one either you could use one of these to turn 12V into 240V AND then the mains adaptor supplied with the display. Less efficient but would work fine.
http://www.maplin.co.uk/Module.aspx?ModuleNo=218810A smaller and more efficient solution (but more expensive) would be to buy a DC-DC converter module. Farnel has them but at a price. You also need a cigar lighter plug etc
http://uk.farnell.com/sunpower/sds-030a05/converter-dc-dc-35w-5v/dp/1254988If the thing does indeed take 30W then probably best not to leave it running for too many hours with the engine off. The battery might have the capacity but car batteries don't tend to live long if deep discharged.