When I set up the R720 with internal SSDs, I used a SATA power splitter, a Y-shaped cable. Today I replaced it because of a known fire-hazard.
I received an email from a reader urging me to replace it and supplied a reference to a known good cable. I happened to have that very cable. It turned out, I needed, and had, two of them.
In general, you want to avoid molded SATA connectors and instead use crimped-on connectors.
The following image is the splitter I removed. You can see it in the photos in the above-mentioned post.
This is the result after I installed the new cables.
For more information on the types of cable you want to replace, search for “sata molex adapter fire”.
This is the cable I replaced it with: StarTech.com 4X SATA Power Splitter Adapter Cable (PYO4SATA).
I had read about this issue before but had still used that cable. I have since thrown all such cables away.