XPS 8940, RAM from XPS 8930 not working (can't boot)

@sfbayXPS I agree with @JOcean , that your 32 GB configuration is not supported. You did not indicate what your 16 GB memory configuration was in your XPS 8940 whether it was 1 x 16 GB or 2 x 8 GB, but there is only two 32 GB memory configurations supported in the XPS 8940, 1 x 32 GB or 2 x 16 GB.

Re: Dell/they simply said 4x8GB configuration is not supported

to give Dell credit, what they actually meant is they have not tested or validated 4x8 Gb Dell ram in XPS 8940 factory configuration.  Since they never did the test, they do not support such configuration.  That statement does not mean it is incompatible.  It only meant you are on your own if you want to do that, whether it would work or not is not supported by Dell (a disclaimer that Dell is not responsible if it did not work), and Dell has no idea whether it would work or not.  

Re: I removed the two aftermarket RAM sticks from XPS8930 and added them to XPS8940. This is when I got the error. I removed the sticks, and then the computer works again.

Dell configuration by default often uses a single lonely 16Gb ddr4 for 8940 (more common than 2x8Gb dual channel).

Re: purchased from Amazon two 8GB sticks (Keusuny brand - DDR4 2666Mhz UDIMM PC4-21300

Mixing the above pair w presumed single Dell ddr4 16Gb seems to be an odd combo, and no wonder it is rejected by Dell bios.  Dell XPS 8940 is completely bewildered by this odd combo of different ram of different speed, latency settings as well as parity (if you indeed have single 16 gb).

But perhaps you have 2x8 gb Dell ram in 8940?  It is still not recommended to mix Dell ram pair with third party pair, and that is most likely why you got no POST.  Your prior luck of mixing ram in 8930 does not extend to 8940.

Re: I called Dell, and they simply said 4x8GB configuration is not supported. However, I have read on this forum that others have managed to make that configuration work.

Dell support is often clueless. They are incorrect by default.  User benchmark has many examples of validated 4x8GB in 8940.

https://www.userbenchmark.com/PCBuilder?searchTerm=XPS%208940%204x8GB

One example of successful 4x8GB is CT8G4DFRA32A.C8FP 4x8GB

https://www.crucial.com/memory/ddr4/ct8g4dfra32a

here is another BL8G32C16U4B.8FE 4x8GB

https://www.crucial.com/memory/ddr4/bl2k8g32c16u4b

@redxps630 @Vic384 @JOcean thanks for your thoughtful responses. I should have mentioned that both my old XPS 8930 and the new XPS 8940 came configured with 2x8GB sticks. So both had two filled and two empty slots. And I am trying to fill the two empty slots with 2x8GB sticks.

Regarding what Dell support said, I was referring to another post that I saw on this subject

https://www.dell.com/community/XPS-Desktops/XPS-8940-memory-upgrade-of-2x8GB/td-p/7779679/page/5

It seems you have also participated in this post. Do you see any merit in getting another brand or speed of 2x8 sticks, or should I just throw out my existing 2x8 and replace with new 2x16?

@sfbayXPS I wish I could say that another brand or speed of 2 x 8 GB may work but I have not seen any posts in this forum where 4 x 8 GB works in the XPS 8940.

Re: Do you see any merit in getting another brand or speed of 2x8 sticks, or should I just throw out my existing 2x8 and replace with new 2x16?

It is safer to get 2x16 or 4x8 of a brand and specific model (Dell or non-Dell) that is validated to work in 8940.  If price is similar then go for whatever you like more.

here are user validated 2x16GB.  https://www.userbenchmark.com/PCBuilder?searchTerm=XPS8940%202x16GB
community recommends crucial ram. Crucial says $back if does not work.

for example CT16G4DFRA32A.M16FR 2x16GB https://www.crucial.com/memory/ddr4/ct16g4dfra32a

here is complete list of crucial ram for 8940

a popular (and more expensive) 2x16 in 8940 is Hynix HMA82GU6DJR8N-XN 2x16GB

https://www.userbenchmark.com/PCBuilder?tab=RAM&searchTerm=XPS8940%202x16GB

Maybe I missed it, but did you mention if the XPS 8940 will boot when only the RAM from the XPS 8930 is installed in the 2nd and 4th slots from CPU in the XPS 8940, without the Dell XPS 8940 OEM RAM installed? And you should also remove the motherboard battery and press/hold power button on front of XPS 8940 for ~30 sec, reinstall the battery, close up and see if it boots now with XPS 8930 RAM. If it doesn't boot that way, the XPS 8930 RAM isn't compatible with this motherboard.

Even if it does boot with only the XPS 8930 RAM installed, it's possible those two sets of RAM just aren't compatible with each other But there is one more thing to try....

Put one of the XPS 8940's original RAM modules in the slot closed to the CPU. Put the other XPS 8940 OEM module in the 2nd slot from CPU. NOTE: These two slots do not have the same color retention clips.

Now put the RAM from the XPS 8930 in the two empty slots, 3rd and 4th from CPU, again with mis-matched retention clips. Then remove the motherboard battery and press/hold power button on front of XPS 8940 for ~30 sec, reinstall battery, close up and see if it boots now.

FWIW, the XPS 8940 motherboard has an odd quirk about where to install RAM, and putting matched pairs in slots with mis-matched retention clips works while putting matched pairs in slots with the same color retention clips has issues...

Below is copied from the specification chart for Dell8940. It lists all supported RAM config. Hopefully you can figure it out from this.

Minimum memory configuration 8 GB

Memory size per slot 4 GB, 8 GB, 16 GB, 32 GB
Memory configurations supported

● 8 GB, 2 x 4 GB, DDR4, 2666 MHz/2933 MHz, UDIMM,
dual-channel
● 8 GB, 1 x 8 GB, DDR4, 2666 MHz/2933 MHz, UDIMM
● 16 GB, 2 x 8 GB, DDR4, 2666 MHz/2933 MHz, UDIMM,
dual-channel
● 16 GB, 1 x 16 GB, DDR4, 2666 MHz/2933 MHz, UDIMM
● 32 GB, 1 x 32 GB, DDR4, 2666 MHz/2933 MHz, UDIMM
● 32 GB, 2 x 16 GB, DDR4, 2666 MHz/2933 MHz, UDIMM,
dual-channel
● 64 GB, 2 x 32 GB, DDR4, 2666 MHz/2933 MHz, UDIMM,
dual-channel
● 64 GB, 4 x 16 GB, DDR4, 2666 MHz/2933 MHz, UDIMM,
dual-channel
● 128 GB, 4 x 32 GB, DDR4, 2666 MHz/2933 MHz, UDIMM,
dual-channel
NOTE: The computer is shipped with 3200 MHz memory.
However, with Intel Core i3/i5 processors, it is limited to
2666 MHz. With Intel Core i7/i9 processors, it is limited to
2933 MHz.

Dell Chris M has published very helpful detailed info including specific manufacturer’s model number for Dell 8-16GB OEM DDR4 in 8940.  
These are Dell validated memory.

It is possible that OP’s 8940 stock ram in system spec says 

As stated in multiple earlier replies, Dell factory configuration “does not support” (has not validated) 4x8GB.  

However, when look at Dell OEM 8GB 9CXF2, one finds one original manufacturer model number HMAA1GU6CJR6N-XN

user benchmark has validated that the same model number 4x8GB works in 8940.

Therefore to answer OP’s most recent question: to get another 2x8Gb or 2x16Gb, there is good evidence that another 2x8Gb of ddr4 either directly from Dell or from third party vendor that says exactly HMAA1GU6CJR6N will likely work.

DK8NX 16GB DDR4, 3200MHz, 2Gx64, Unbuffered, 288 pin, Single Rank, 1.2V, Non-ECC, Non-Encrypted Adata AO2P32NCSV1-BEVS, Hynix HMAA2GU6AJR8N-XN/HMAA2GU6CJR8N-XN, Kingston KDK8NX-MIB/KDK8NX-MIE, Micron MTA8ATF2G64AZ-3G2B1/MTA8ATF2G64AZ-3G2E1, Samsung M378A2G43AB3-CWE/M378A2G43BB3-CWE

C5N22 16GB DDR4, 3200MHz, 2Gx64, 2RX8, Unbuffered, 288 pin, Dual Rank, 1.2V, Non-ECC, Non-Encrypted, Adata AO2P32NCST2-BZ7SHD, Hynix HMA82GU6DJR8N-XN, Kingston KC5N22-HYD/KC5N22-MIE, Micron MTA16ATF2G64AZ-3G2J1, Samsung M378A2K43EB1-CWE

9CXF2 8GB DDR4, 3200MHz, 1Gx64, Unbuffered, 288 pin, Single Rank, 1.2V, Non-ECC, Non-Encrypted Adata AO2P32NC8W1-BD3SHC, Hynix HMAA1GU6CJR6N-XN, Kingston K9CXF2-MIB/K9CXF2-MIE, Micron MTA4ATF1G64AZ-3G2B1/MTA4ATF1G64AZ-3G2E1, Samsung M378A1G44AB0-CWE/M378A1G44BB0-CWE

V0M5R 8GB DDR4, 3200MHz, 1Gx64, 1RX8, Unbuffered, 288 pin, Single Rank, 1.2V, Non-ECC, Non-Encrypted, Adata AO2P32NC8T1-BZ5SHD, Hynix HMA81GU6CJR8N-XN/HMA81GU6DJR8N-XN, Kingston KV0M5R-HYD/KV0M5R-MIE, Micron MTA8ATF1G64AZ-3G2J1, Samsung M378A1K43EB2-CWE

When looking at another Dell OEM 8GB ddr4 for 8940 V0M5R, one sees another original manufacturer model number Hynix HMA81GU6CJR8N-XN

user benchmark has also validated the same exact model number 4x8GB works in 8940.

V0M5R 8GB DDR4, 3200MHz, 1Gx64, 1RX8, Unbuffered, 288 pin, Single Rank, 1.2V, Non-ECC, Non-Encrypted, Adata AO2P32NC8T1-BZ5SHD, Hynix HMA81GU6CJR8N-XN/HMA81GU6DJR8N-XN, Kingston KV0M5R-HYD/KV0M5R-MIE, Micron MTA8ATF1G64AZ-3G2J1, Samsung M378A1K43EB2-CWE

conclusion: OP’s issue was because of using non validated 2x8 gb “purchased from Amazon two 8GB sticks (Keusuny brand - DDR4 2666Mhz UDIMM PC4-21300” in combination with Dell validated 2x8 GB DDR4 3200 MHz (PC4-25600)

suggestion to OP: get two additional Dell OEM 2x8 Gb that matches current Dell 2x8 Gb in DP/N.  either 9CXF2 or V0M5R.  better do not mix up the Dell ram.  If you already have 9CXF2, then get the same part (same goes for V0M5R). look at your physical Dell ram for DP/N or look up your system spec using service tag.

or get 2x8 Gb with exact model number:

Hynix HMAA1GU6CJR6N-XN (if you have 9CXF2) or 

Hynix HMA81GU6CJR8N-XN (if you have V0M5R).

Let's all keep in mind the specs only list RAM configurations that Dell actually tested and validated in that specific PC model.

That does not mean other configs and/or other brands of RAM won't work, but Dell isn't responsible if untested configs/brands don't work. So Dell Tech Support and forum moderators are never going to publicly mention any configs/brands that Dell hasn't officially tested...

There are threads saying 48 GB of RAM will work in the XPS 8940, but that's not one of Dell's validated configs. That doesn't guarantee the (unlisted) 4x 8 GB config will work or if Keusuny RAM @sfbayXPS installed will work either alone or when used together with Dell OEM RAM.

So the first thing we need to know is if the 2x 8 GB Keusuny RAM works alone in the XPS 8940...

Thanks Ron,

Your tip regarding mis-matching the slots was golden.

I bought 2 8Gb sticks from Dell, with almost identical figures when comparing existing and new in CPU-Z. The originals are Samsung, the new SK Hynix.

Absolutely nothing when trying to boot in matching slots, but after switching around it booted up after a short delay. Dell 8940 4x8Gb - happy days!

@akaAlso  - Glad that worked for you too.

What speed is the RAM is running at using CPU-Z (free) on the Memory tab? And also check to see if it's running in dual channel mode (= Channel # on CPU-Z Memory tab).