As @azzAz says that wire is scorched a bit near the 1x PCIe connector. It looks like it overheated. Probably not enough power to the riser or a surge.
USB pcie risers run 1x yellow power wire (12v) and 1x red wire (5v) into the Molex connector. That cheap ass ribbon cable you bought has a single power and no ground wires. Heck, it probably cost you as much as a good PCIe USB riser would.
I sell PCIe risers so take my advice with a grain of salt, but don't you think it's weird that your Molex connector usually has 4 wires running into it but you only have 1 in your ribbon riser?
Best guess is they don't provide a return path for the ground. It's having to ground thru those very small ribbon cables. That's the poorest design I've ever seen. At minimum It should have had a ground accompanying the yellow power wire. I can't say as I've ever seen them made this way. For example something like this.
The more I dig thru eBay. I can't find any with only one wire. 16x-16x also has power and ground.
Edit some cool stuff coming on pcie 4.0.
