adding RAM to xps 8940

I would suggest that you make sure that the RAM you purchase is the same (1Rx8 or 2Rx8) as the existing RAM to ensure compatibility. If your system is under warranty then the reason for Dell RAM would be that it would also be covered under the warranty where any non-Dell RAM modules would be covered under the RAM manufacturer's warranty but not Dells. As far as the slot, since the RAM you have now is in slot 2 then the additional RAM would go into slot 1 (white with white then gray with gray tabs). This YouTube video may help and notice in the video the author does not use Dell RAM but a quality RAM nonetheless. However that video assumes you would be replacing both RAM modules. Since you have Dell RAM compatibility would best be achieved with additional Dell RAM. Next best compatibility would be Crucial RAM here which is guaranteed compatible or it can be returned.

Is it (1Rx8 or 2Rx8)  is a good question, all I have as info is what was on the purchase bill which is detailed in original post.  Any idea how I can find out which I have?

I suspect you are out of warranty by now so I'd go for upgrading to 32GB Dual rank RAM.

I have the same system, and I had a single 16GB stick, and it was SINGLE RANK.

First, you should match 'pairs', sometimes different RANK or BUILD dates don't work well together. Sometimes they do.

I do suggest going here, https://www.crucial.com/store/systemscanner, and run the scanner (for some reason it isn't working for me now) but I bought (on Amazon due to the free shipping) 2 16GB RAM as a matched pair. Just swap out the old one and put one in that slot (should have a White tab) and the other in the other White tab slot.

Ones I get were CT16G4DFD832A (2 stick kit had a different number though and I didn't keep the outer wrapping). That is why mine ended in 832A vs, A32A on Amazon and also probably Crucial's site? Good thing with Amazon, put the sticks in, can't boot, easy return.

Can get it at Amazon now for $59.99 (https://www.amazon.com/Crucial-2x16GB-Desktop-Memory-CT2K16G4DFRA32A/dp/B08C4LXXCJ/ref=sr_1_5?crid=3SIMP3QWUBU1G&keywords=CT16G4DFD832A&qid=1700411289&s=electronics&sprefix=ct16g4dfd832a%2Celectronics%2C86&sr=1-5 ) or Crucial, but run the Scanner there, as it seems to not be available there? There are others, so maybe that is why the scanner couldn't work for me, maybe it will for you?

@danielf​ 

Look on the stick itself, look for 1R or 2R in the part number usually.

2R or Dual Rank is 'better', but that is subjective as you might never notice the improvement. Mixing them will surely keep you at the lowest.

Don't want to pull the stick to tell, use CPU-Z and look at the SPD tab:

By the way, Micron IS Crucial.

@danielf​ Generally look at the sticker on the RAM stick. This page at Superuser may help. You can also download Hwinfo here and it will display all you need to know about your RAM including the number of ranks (i.e. 1Rx or 2Rx).

thanks all,  the needed info was on the ram stick:    2Rx8

@danielf​ Happy we could help out!

If you are populating just 2 slots total dual rank, if you want to use all 4 slots use single rank.  outside of that make sure they jedec at 1600mhz so you get the full 2999 mhz . Since the Dell motherboard cant actually use the memory at 3200mhz.