XPS 8940, upgrades, ram, USB-C card, storage

Dell validated 32 gb ram: 732YD 32GB DDR4, 3200MHz, 2Rx8, Unbuffered, 288 pin, Dual Rank, 1.2V, Non-ECC, Non-Encrypted, Hynix HMAA4GU6AJR8N-XN/HMAA4GU6CJR8N-XN, Micron MTA16ATF4G64AZ-3G2B1/MTA16ATF4G64AZ-3G2E1, Samsung M378A4G43AB2-CWE

you do not have to buy directly from Dell if you can find someone parting with their Dell 32 gb ram of same DP/N or model.  732yd dell price $330, eBay new price $150.

any 2.5 sata ssd would work with your pc.  your pc should have sata data cable and power connector already laid out.  If you do not have an empty 2.5 caddy then get one on eBay for 8940.

On a pictures by @redxps630 above you can notice there's no VR heatsink installed therefore in this particular example making upgrade pointless since PWM system will keep thermal-throttling CPU down, most of the time turbo-boost (both versions) will be for a very short duration.
Higher load and consequently temps without relevant heat dissipation will lead to much shorter motherboard component lifespan.
But I would expect BIOS logic to detect absence of heatsink and either prevent boot beyond certain point (apart from initial messages / basic functionality) or disabling higher end performance options automatically.

Hopefully since OP purchased i9-11900k config from Dell the rig ought to have high end tower cooler and VRM heat sink already installed.

@STEPHEN PERIDORE  Crucial lists CT2K32G4DFD832A as compatible with the XPS 8940. 

What config is your 64 GB of RAM now, 2x 32 GB or 4x 16 GB? If you have 4x 16 and you're willing to try 96 GB (total) you could just get 2x 32 GB and keep 2x 16 GB.

NOTE: You may have to install the RAM in "mixed" pairs to achieve full speed with 2x 16 + 2x 32 GB (96 GB total). In other words, put 2x 16 GB pair in slots with different color retention clips and put 2x 32 pair in the other slots with different color clips. This is how other XPS 8940 users get RAM to run at full speed after installing 2 different brands (eg, Dell OEM + other). 

The XPS 8940 appears to support PCI-e 3 while that card supports PCI-e 4 (but should be backward compatible with PCI-e 3). So you probably won't get max rated speeds from the card.

What version of BIOS is installed on this XPS 8940? Some users have reported issues using the PCI-e x4 slot after updating XPS 8940 to BIOS 2.2.0 or higher. So it may be hard to predict if that USB-c card will work or not.  And you can't revert to any BIOS lower than 2.2.0.

BTW: If BIOS is set to RAID now, you may want to change it to AHCI because some SSDs don't work well when it's set to RAID. But...you cannot just change that setting in BIOS. You have to reconfigure Windows to use AHCI before changing that BIOS setting or the PC will become unbootable. Easy to configure Windows for AHCI without having to reinstall...

RoHe, redxps630, & sam55todd, 

Thank you very much for your very detailed and thoughtful feedback.  I currently have 4 x 16G = 64GB installed.  I was just planning to replace the four 16GB modules with four modules of:  32GB UDIMM / DDR4-3200mhz / PC4-25600 / CL22 /  unbuffered / Non-ECC / 1.2V / 288pin (CT2K32G4DFD832A).  Crucial states that these modules will downclock to 2933/2666mhz due to i7/i9 processor limitation.  

My Dell XPS 8940 manual states that I have ONE PCI-e x 1 slot, ONE PCI-e x 4 slot, & ONE PCI-e x 16 slot, all of which are gen 3.0.  My graphics card is a NVIDIA GeForce RTX 3060 12GB (see screenshot of specs) installed in the PCI-e x 16 slot, so apparently, I only have the PCI-e x 4 & PCI-e x1 slots still available.  I think the Sonnet Allegro USB-C 4-port PCIe card that I'm interested is inserted into the PCI-e x 4 slot.  This 4-port USB-C has dual USB 3.2 Gen 2 Controllers providing up to 7.5w per port.  
https://www.amazon.com/gp/product/B07L8KCQPT/ref=ox_sc_saved_image_2?smid=AFZIU1SXEW341&psc=1 

Sam55todd, you point out that if I don't have a VR heatsink installed, my upgrade is "pointless".  Which upgrade?  The RAM, the USB-C PCI-e card, or the internal Samsung 870 QVO SATA III 2.5" 8TB SSD drive?  I'm not sure if I have a VR heatsink installed.  I've neither opened up the tower nor do I know how to identify a VR heatsink:-(

Lastly, as an alternative to the Samsung 870 QVO SATA III 2.5" 8TB SSD upgrade option, because M.2 PCI-e drives are much faster, I'm thinking about swapping out my 2TB M.2 PCIe NVME SSD boot drive for an "Inland Platinum 8TB M.2 NVMe 2280 PCI-e Gen 3.0x4 3D NAND Express SSD drive (R/W up to 3300/3000 mb/s; 1800 TBW; PCI-e express 3.1;  NVMe 1.3 compatible).  Is this model compatible with my Dell XPS 8940 system?  If it is, aside from cost ($1099), would you recommend this upgrade?  The identical 4TB model is much cheaper at $469.

https://www.amazon.com/Inland-Platinum-Internal-Compatible-Solutions/dp/B093B7GQBQ/ref=sr_1_1_sspa?crid=2EA88IIQ1IF6U&keywords=4tb%2Bm.2%2Bpci-e%2Bssd%2Bdrive&qid=1654720914&s=electronics&sprefix=4tb%2Bm.2%2Bpci-e%2Bssd%2Bdrive%2Celectronics%2C112&sr=1-1-spons&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzNThYUUdHN1U5WDAzJmVuY3J5cHRlZElkPUEwMjk1NTI2UDBHTjg4Qk1KWENRJmVuY3J5cHRlZEFkSWQ9QTAxODUyNDRHMkdUTlFHTlUwM1Mmd2lkZ2V0TmFtZT1zcF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl&th=1 

@STEPHEN PERIDORE The 8 TB NVMe drive may be compatible but Dell only specs and verifies drives up to 2 TB. Is your requirement for speed really worth the almost $400 difference between the Samsung SATA drive and the Inland NVMe drive? 

Re: I'm not sure if I have a VR heatsink installed.  I've neither opened up the tower nor do I know how to identify a VR heatsink:-(

if you plan to upgrade ram you will have to open the case.  the VRM heatsink is to the left of CPU cooler.  it is present in the last pic I illustrated to the left of high end tower cooler. 

  I presume since you have the high end -k cpu you should have both already.  another way is to look inside your product spec if you type in your service tag on Dell support.

@STEPHEN PERIDORE  That's a big price for the 8T NVME SSD. Do you really need so much storage space? And how much extra heat is it going to generate?

FWIW, Dell's specs only list what they actually tested/validated for a given PC model. So just because an 8T SSD isn't listed, that doesn't mean it won't work, but the specs mean Dell isn't responsible if it doesn't work.

Yes, the Crucial RAM will clock down to the "allowed" max speed. The XPS 8940 is actually shipped with 3200 MHz memory, but with Core i7/i9 processors, it runs at 2933 MHz, max. 

Only you can decide whether to replace all four 16 GB modules with four 32 GB, assuming you really need 128 GB of RAM.  I gave you a less expensive alternative to try 96 GB total, 2x 16 + 2x 32, to see if that's enough RAM, before buying another 2x 32 GB. And you can always sell either two or four 16 GB modules to earn back some of your upgrade costs.

That USB-c card should go in the x4 slot.

I got the courage to remove the CPU cover and have verified that my unit has a VR heatsink.  Does that mean my upgrades (RAM>>128GB / 4 or 8TB M.2 PCI-e / 4-port USB-C 3.2-Gen 2 PCI-e x4 card)  won't be problematic?

Ron, thanks for the RAM options you propose.   If I settle for the Samsung 8TB 870 QVO 2.5" SATA III SSD to be placed in the available 2.5" HD chasis, would there be an issue with excess heat?

I think you make a very good point.  The additional $400-500 just for speed alone may not be worth it.  The Samsung 8TB 870 QV0 2.5"  SATA III SSD has the same amount of storage and would last for years, and the speed is still significantly better than older 7200RPM hard drives.

Re: I got the courage to remove the CPU cover and have verified that my unit has a VR heatsink. 

based on your photo you already have all the cables and caddy for a 2.5 sata ssd.

when purchasing 4x 32gb ram, try to match the oem model number exactly with Dell Hynix HMAA4GU6AJR8N-XN/HMAA4GU6CJR8N-XN, Micron MTA16ATF4G64AZ-3G2B1/MTA16ATF4G64AZ-3G2E1, Samsung M378A4G43AB2-CWE.

e.g. https://www.ebay.com/itm/115400318445?hash=item1ade651ded:g:zFAAAOSw2s1ikORO

MTA16ATF4G64AZ-3G2E1

If seller accepts return that would be good in case the ram does not work out.

@STEPHEN PERIDORE  An 8T  SATA SSD probably won't generate as much heat as an 8T NVME SSD. And, the SATA SSD isn't directly attached to the motherboard like an NVME SSD, so less heat on the motherboard, and there's probably more air circulation around the 2.5" drive bay.

You could always install something like Speccy (free) and set it to load at boot. It puts a temp icon in the notification area of the taskbar so you see CPU temps all the time, and mousing over that icon pops up a bubble with other monitored temps, eg: GPU and drives.

Stephen

Did you ever figure out if the Sonnet Allegro USB-C 4-port PCIe Card was compatible with your system? I'm looking to add USB 3.2 port card to my system, which is the same system you have.