Need advice on type of M.2 SSD and respective adapter to purchase according to available connections :(

Hi all.

I need some tech savvy assistance and counseling. I posted on r/techsupport but got no replies: First attempt at asking for help.

What I have: I have a Dell XPS 13 (Amazon product page and Dell website PDF manual) using a 128GB M.2 SSD, and a desktop with a 1TB HDD using a Gigabyte GA-Z170-HD3 motherboard (Amazon product page).

What I want to do: I want to switch out the SSD in my laptop with a newer larger one, and install the old SSD into my desktop with an adapter as the new default C: drive.

Why I need help: I've been looking for adapters and M.2 SSD's and it's a really complicated topic because apparently there are 3 varieties of M.2 (why is it so complicated?) and the differences are how they're keyed: B, M, B+M. There's supposed to be a performance difference between these and they're also limited by the slot: from what I understood if I purchase a powerful M.2 SSD and the slot won't allow higher speeds it's wasted money. Oh, and also there are different M.2 sizes too, haven't found any reading material concerning performance differences; I could be uninformed and messing it up. In the end I'm not sure of the conclusions I made from what I read and that's why I posted here asking for help and advice.

What I was looking at so far:

• Samsung 850 EVO - 250GB - M.2 SATA III Internal SSD (MZ-N5E250BW) (Amazon product page).
• Newer SSD for my laptop. Unsure if it's the right keys for the slot in the laptop's motherboard. Could use help confirming this.
• StarTech.com PEX4M2E1 X4 PCI Express to M.2 PCIe SSD Adapter, M.2 Ngff (NVMe or Ahci) Card (Amazon product page).
• M.2 adapter for laptop SSD that is supposed to go to desktop motherboard. Is it the right one?

Most importantly, I forgot to ask the obvious questions:

• Is this switch and replace possible? Will it work?
• Can the SSD on my desktop hold the C: drive with the Windows dir with the proposed adapter configuration?

A friend told me that 128GB isn't practically enough space, which I agree with; more so since I have +80GB Dropbox cloud. To address this I'll end up hard linking the folder to the 1TB HDD.

I really appreciate any help. Hope it's not too much info. Thx in advance.