@cannedheat0 No, your PC will not be faster because the maximum RAM speed spec for the XPS 8900 is 2133 MHz. In fact, your PC may be slower with Photoshop because you will have less memory to work with, and with less memory, your PC may have to swap memory to disk. If you want more speed, get a solid-state drive if you are already using one.

No, you won't get more speed because the max memory clock for XPS 8900 is 2133 MHz,  your 32 GB of 2400 MHz RAM got downclock to 2133 MHz.

It's better to keep your total RAM of 40 GB.

Thanks both.  Very helpful.

Today it was suggested to me that I should use DDR5 in the 8900.  My research shows it will probably not work.  Any advice?  Thanks.

There is Dell Specs with validated support configurations, and there are users validated configurations.  Some upgrades can work beyond and different from original configurations.  You can find yours but within a logical of technology supported.

The motherboard has a fixed chipset (non-upgradeable), which will support certain generation of CPU.  The processor determined the compatibility of memory types.  Sometimes, you can mix and install memory beyond Dell tested configurations but can not get beyond hardware compatibility.

While installing faster DDR4 in your system will work with force downclocked, DDR5 could rendered a non-bootable machine.  

Beside seeking to expand memory in your system, you did not mention any performance issue or productivity problem.  If the machine is still viable for your needs, use it the way it is.  Any upgrade budget, saving it toward your next machine. 

@cannedheat0 DDR5 will not work. I am pretty sure you can't even put DDR5 in a DDR4 slot because the key locations are different if your memory slots are keyed.