Just because a RAM config isn't listed, that doesn't mean it won't work. Dell only lists RAM configs they've tested/validated in this PC model.  That said, there's no guarantee 80 GB will work, unless you find a thread where somebody has installed 80 GB in XPS 8950. Assuming it boots and runs with 80 GB, check RAM speed and channel mode to see if it's running at the expected speed. You can use CPU-Z (free). Specs say XPS 8950 with 2x 32 GB runs in dual channel mode at 4400 MHz, regardless of the RAM's (higher) rated speed. So you might see 4400 MHz, or possibly only 3600 MHz. We don't know the cut-off between 4400 MHz and 3600, MHz, just that 4x 32 GB runs at 3600 MHz. Post back and let us know what happens...
I have a new XPS 8950 that originally shipped with 2x8GB DIMMs. I since purchased 2x32GB 4800 MHz DIMMs from Crucial. One was bad, so for the moment I'm successfully running with 1x32GB DIMM. Once I get the replacement 32GB DIMM I'll be able to do the supported 2x32GB configuration. Just curious I'd be able to make use of the original 8GB DIMMs for an 80GB configuration. It's not listed as a supported configuration, but just curious if anyone else had tried this? Thanks!
XPS 8950, 80GB ram configuration?