I assume you're talking about the 12V DC-DC adapter (aka 'egg'). Those are known to be unreliable. You'll be better off using one of the many 12V regulator options mentioned in the forums. If you're using it with a carPC, the easiest solution is to power your screen directly from the 12V output from your computer supply.
Concerning using the power supply, (using an OPUS 90W) I notice that the picture is distorted when not going through the "Egg" power cable. It appears that that the circuit some how cleans up the video.