Thank you for the link!
Yeah I think it could be anything really... I might try buying and open it to see what could it be (it's on auction right now for some bucks).
Thank you guys for the answers! I thought it was strange that I couldn't find any mod with this cable in the internet, and...
I saw this PS1 on sale with a description that looks like this: "PS1 Phat with HDD connector cable"
Apparently its laser is broken but I can't recognize the cable in the pictures, it's a SCPH-9001 NTSC-U model.
Could somebody with more experience with PS1 mods help me figure it out? It's not a...