I don't find several, I find two on the Dell site. One is a four-port one, the other a single. The one I have looks like this:
[Link: accessories.us.dell.com]and is the only one they had a year ago.
www.keyspan.com takes you to tripplite.com...from there, a search for "serial" and adaptor" yields nothing. Even a search for "adapter," which is the way they spell it, yields nothing, even though the site clearly has those words on it. Maybe yo uhave to know the model number to find the model number. Yes, I'm being critical of their site.
You want the U-209-000-R, which you can link to from
[Link: tripplite.com]You probably didn't recognize which one you wanted because it wasn't apparent that you wanted USB A to DB9 Male. I'm not sure I would have known, either.