Probably about a month or two ago I got my 360 back from microsoft for RRoD. The easiest way to find out if you had one of the newer models was to check the voltage. It couldn't hurt to hope microsoft would bless me with the new jasper model as compensation for waiting to have my system fixed. But of course it was the same power hungry model as before, so who knows how long my replacement will last.
Just look at your power Connector. That will tell you right away. Your power connector looks a little different See Image Below
(http://www.blogcdn.com/www.joystiq.com/media/2008/12/newjasper1.jpg)
Then If you’re considering a new console, look for “12,1A” where the power information is listed on the back of the box.