Excellent question.
This ac adapter is unique and finding the exact replacement
is difficult. However, it's not impossible. I've posted a similar
question on a laptop website to see what answers are received
since this question will close in a day.
http://www.netbooksmalllaptops.com/where-to-find-an-ac-adapter-for-an-alienware-area51-m17x-laptop.html
What I'm going to have to find out is if your adapter has the 4 pin connector
or the barrel style plug for the laptop. Hopefully I find out before this question ends.
Otherwise, I post the answer on the other place.
P.S. I never thought there would be a difficult ac adapter question.
Thanks for this question and the challenge!
P.S.S. The four pin DIN Dell part number is 0405B20220.
Hiport is a brand listed on Amazon.