They are 12V fans so I soldered them to the 12V output that also powers the HDDs.

I could, yes. The laptop has an M.2 slot that is intented to be used for M.2 SSDs, maybe you know them, they’ve gotten very popular. Almost any mordern motherboard has space for them.

But instead of putting an M.2 SSD in that slot, I bought this adapter with SATA ports. And this adapter fits exactly in the same spot as the SSD could have. Then the SATA ports of the adapter can just be used as regular SATA ports as on any motherboard.

Did you read the whole post? I thought I made clear what I did.