12v 500ma is about 1/2 of what you need to run that box, if it asks for 12v 1200ma... you need a bigger power supply.
At one point, I used an Audio Authority VGA-to-component video converter to do the opposite of what you're wanting to do - that is, send the output of a computer to a Component-input-equipped TV. It ran about $120.
Now, looking at component/S-video to VGA converters, the reverse of my setup (and apparently what you need with that Samsung) - you're talking 2x the cost. That's ridiculous for what you need, I think...
I have three monitors - a Dell and two Lenovos - that take component (YPbPr) video directly from my Panasonic AVCHD camera, via analog cables (or HDMI).
So, I think that, if you can't get the Samsung to work w/o a converter, it might be cheaper to buy a new LCD panel?
Sorry, wish I could be more help!
-Don