What is the current RAM configuration?
Current one is the inbuilt one that was shipped with the laptop
View: https://imgur.com/a/t8NbbM7
Module specs and sizes: did you mix and match 4 GB with the new/added 8 GB module? Or some other combination?
No, I matched 2x8 GB cards, one inbuilt and one purchased
The only way to know about the RAM compatibility is to go to Dell's website and find the applicable specs for the laptop or its' installed motherboard.
[Note: you can use RAM manufacturer's websites to help establish compatible RAM. However, that is more of a consensus approach versus actually getting the information from Dell.]
There should be some documentation regarding supported RAM modules and what combinations are supported thereafter. Laptop specs and/or User Manual. Details matter. Supported RAM could vary by model, version, even serial number....
The only way to know about the RAM compatibility is to go to Dell's website and find the applicable specs for the laptop or its' installed motherboard.
I used the Dell compatible upgrades, listed my laptop and it does show the ram card as a compatible upgrade, not sure If I understood you correctly though
I used Crucial's compatibility tab and the ram shows up as a compatible one as well