As [NAME]  posted, never a good idea to mix DIMMs. They should be EXACTLY the same part. If you must use 2 different pairs, you might get by with each pair being in the same "memory bank" (notice color of DIMM retention tabs). Turn off all over-clocks (at least CPU and RAM). Machine is way fast already. Plus, it will Turbo-Boost itself when safe to do so. Don't you want stable/reliable over 4% faster ? First, ram/machine should pass (long) ePSA ram test. In view of recent trouble ... then run bootable www.memtest86.com . If you can get 2 perfect long passes with that also ... it should be working 100% in Windows. Since Aurora-R3 ... Aurora's they have never really tolerated miss-matched DIMMs.  So, as I have been posting for about 9 years now ... Most owners should just go ahead and get the desired amount of RAM pre-installed from Dell/Alienware build-factory. Apart from high (or prefect) compatibility ... they will carry the same warranty as the machine. RAM won't be an issue and you can just use this nice expensive machine you just bought. Life is short.    
Aurora R10 Ryzen 9 5900X / Radeon RX6800 XT / 32Gb 3200MHz (16x2) Decided to add extra 32Gb RAM, so bought the same Kingston Fury RAM, same speed, and proceeded to fit it. Initially it worked, thought all was well. However booted up day 2 and played Forza 5 Horizon and the game wasn’t running well. A few stutters and black screen moments, so I decided to head into Alienware Fusion to check settings. Decided to turn off RAM O/C. Rebooted. Blank screen. No amount of reboots would bring up video. In the end I googled for a while and found what I believe to be the issue. The power button was flashing yellow twice, but given the FX mode was rainbow it was hard to tell exactly whether it was just ‘2’ or ‘2/1’! So at this point I know it’s either the RAM or a failed board. Neither are good news, but it’s a handy feature that at least gives you some indication of where to start your testing. As I’d added more RAM my first port of call was to remove it. So I did. Still nothing. So I’m now even more concerned it might be the board. I Google some more, and find the following information: The Dell Fury RAM modules are effectively ‘OEM’ spec, and whilst the aftermarket RAM matches the majority of the spec sheet, the tCL / tRCD / tRP figures differ between the two sets of RAM modules (Dell figures were higher). Eventually I got video back by performing a flea power drain, and removing the CMOS battery. Finally some good news, video returned. However I could only run one set of RAM chips or the others, not both in ANY slot configuration. I’ve decided to fit the aftermarket 2x16Gb do Fury 3200 ram (15/17/17), and I’ve just ordered another 2x16 of exactly the same model from the supplier so I can hopefully run a full 64Gb without conflict. I’m guessing this is either a BIOS or XMP related incompatibility issue, but something that you would hope in these modern days that would cause something as catastrophic as a loss of video. No amount of attempts to press F12 at start up for bios access or f8 prompted the video back, and only the CMOS battery removal for a bios reset resolved the issue. It’s really disconcerting having no video as this outcome for this fault as it leaves you thinking it’s GPU or motherboard issues rather than a basic RAM fault. Why it kills the video?? The good news is the R10 is back up and running and has passed diagnostics checks. Whilst I don’t require any additional support on this issue I wanted to share my experience in case it helps anyone else in the future. It’s been a stressful afternoon, and whilst I’m not a complete IT novice the experience felt a lot harder than I’d have expected for something as basic as a RAM upgrade. Every day’s a school day!  
Aurora R10, factory vs aftermarket RAM compatibility issue, loss of video