It’s the PCIe cable, and an older power supply, the Corsair HX1050. On the side that plugs into the PSU, the far right pins have no electrical going into them. I’d ordered some extra cables, and not sure if I got the wrong thing but these cables have 1 wire going into 1 of the 2 blank pins. I’m really confused.
There is a 6-pin and 8-pin version of those connectors. There are also low-power and higher-power versions of the 8-pin ones. You may have the low-power-only version of the 8-pin cables? The extra pins are a ground and sense pin, and allows more power to be sent through the other 6 pins, if connected. The missing pin in your blue connector seems to be the extra Sense pin.