Had the same problem with my 7550. Ordered 32GB from Crucial to add to the original 16GB that came with the system. They did work but the timing went down to ~2166MHz instead of the 2933MHz. Can't say that I noticed the difference, but did end up biting the bullet and removing the keyboard and just use the crucial modules which run at the correct speed installed by themselves.
I have a question with the battery LED diagnostic code on my Dell Precision 7550. I am getting 2 blinking ambers and 8 whites. Looking at the dell documentation that popped up in google, there is no codes for 8 white blinks. Wanted to have an idea of what was going on before I call customer support. Dell Command Update indicates there are no available updates.
A reference guide to the Precision Mobile Diagnostic Indicators | Dell US