Question: How big of HDD can I add to my Dell XPS 8500 as a secondary drive. It runs Windows 10 64bit 12 gig Ram and currently has 1 TB Samsung EVO as primary drive

Answer:

How big of HDD can I add to my Dell XPS 8500 as a secondary drive. It runs Windows 10 64bit 12 gig Ram and currently has 1 gig Samsung EVO as primary drive

“1 gig Samsung EVO”
Typo? Should be 1TB?

As a secondary drive, you should be able to use just about anything SATA III.