The only thing I can think of is that it has a physical 6-pin connector, but the power pins aren't connected?

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I think we might have a winner here. I looked at the description on one of the listings and saw this:

Contacts 6 pin to 6 pin (no power)

Seems a bit odd, but hey it's cheap Chinese cabling. So I'll just look for a more "deluxe" cable.