lenovo thinkcenter

So, I have this lenovo m900 SFF and I'm having an issue with finding the right sata power cable for it since it's a proprietary cable ( square 4 pin ) so I saw this particular one 8 pin dual sata cable. Is it safe to use this for my m900? or will this cause a problem?

I've fairly new in computer my problem is that I have a Lenovo m900 sff and I wanted to upgrade its TFX PSU to an ATX one since atx has a higher voltage so I can add a dedicated GPU. will this cause any issue for my Lenovo motherboard?

I'm thinking about buying a used Lenovo Thinkcentre e73, with a i5 cpu and upgrading the gpu for some gaming. I've seen some posts about upgrading this computer model and some of them talk about the power supply not being able to supply enough to some gpus. What if I also upgrade the power...