Well, not sure if Dell is any different, but from my experience, you can use any OEM version at any kind of PC. As long as the standard policy (one serial per PC) is fulfilled. Aka you stop using the PC you got the serial from.
I got several OEM versions over the years from several brands (like acer, samsung, hp) and used all of them afterwards on a different, custom PC without issues. Just make sure the site you want to purchase them from is legit.