The 6 pin peripheral connectors on the power supply do not match the pinout of the 6 pin Pcie male connector.
Google the power supply connections and you will see. For instance, pcie 8-pin has a ground and sense pin at the end then 6-pins with 3 + on bottom and 3- on top. The CPU connector is different and the polarity is reversed, 3+ on top and 3- on bottom. The peripheral connection is even more different with blank pins and top and bottom interleaved. Google the connections and you’ll see.
P.s. That’s why you may find it hard to find a 6 pin male to male cable (except for maybe a mac or i-apple).
You can use the 8 pin to 4+4 CPU cable with adapter to rewire it to 6+2 pin pcie. It is basically a splitter that fits the end of the 2nd cpu cable and adapts it to pcie. Available on Amazon.