I have this USB C coupler to connect 2 USB C cables. The coupler has 2 female connectors:
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I use it to extend my cables when charging:
But it doesn’t always work. Sometimes it does, sometimes it doesn’t (e.g., the device is not charging).
So I assumed this coupler was defective, and got another one:
This one has a small LED, and it too wouldn’t always work.
But because of the LED, I quickly figured it out:
If the LED isn’t on (e.g., not current is flowing), I just have to flip one of the male connectors 180°. Then it works.
And that’s what I also have to do with the first coupler I got: if it doesn’t work, flip one of the connectors. I just needed a LED to figure this out 
Article Link: Quickpost: USB-C Couplers | Didier Stevens