Question About DELL Precision M6400 AC ADAPTER??

Well I build a precision m6400 fom scratch by ordering different piece of the computer. my question is this. i need a ac adapter but everything i find online shows the ac adapter with some kind of circuit board that lookslike it plugs into the system board. what is that board? here i a link to the website were the acadapter and board is.
http://cgi.ebay.com/New-Dell-PA-7e-...QQptZLHQ5fDefaultDomainQ5f0QQsalenotsupported

look at the pic and you will see the little circuit board. what is that for?

 

I think it's a mistake. It's probably supposed to be a picture of the power cord, but the seller messed up. I'd contact the seller just to be sure, though; maybe it's actually something important.