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?