Help for SSD specs in my XPS 8900

I want to get a new SSD for the M.2 slot on the mobo but are not sure what will fit.
So could someone tell me the SSD specs for my system:

Like what is the PCEi rating for the M.2 slot?

Dell XPS 8900
Purchased Jul 2016
I couldn’t find any help with the documentation that came with the PC so the following are from the stickers and IDs:
MoBo: 0XJ8C4 R46NM
The SSD slot: M.2 SLOT2
From the sticker on the bottom of the tower:
• Reg Model: D14M
• Reg Type: D14M002
• MSIP-RMM-E2KD14M002

For example I looked at a WD Black 512GB Performance SSD - 8 Gb/s M.2 2280 PCIe NVMe Solid State Drive – WDS512G1X0C.
• Will it fit and work in my M.2 slot?
• Or would it be better to get an M.2 adapter and put it in the spare PCEi slot?

Suggestions appreciated

(Got some pics of the slot but can't see where to upload them??)