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I'm wondering if asymmetric charging behavior (does it differently depending on which orientation is used on the cable connector) is a feasible failure mode with USB C, which is supposed to be an asymmetric port.

What got me wondering is the behavior I'm getting from a recently replaced USB C charging port. Every cable I've tried now gives me a "charging slowly" dialog from only one of the two orientations.

I just assumed this was due to one of the pins being messed up on the new port. The techs were totally flummoxed by this though, and I had to demonstrate it to them on their own equipment. They went ahead an ordered a new part for me, but insisted this shouldn't be possible.

enter image description here USB C pin layout for reference

Are they right about how weird this is? I think my bent pin theory holds, since it looks like there are copies of each kind of power-related pin (2 VBUS and 2 GND on each side). However, I don't know exactly how those pins are typically used. If both sides are used to deliver power simultaneously, then it seems like the power input ought to be additive, and the techs are right that this shouldn't be happening. If they are instead merely redundant, and only one set is used depending on the orientation of the cable's plug, then what I'm seeing would make sense.

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  • \$\begingroup\$ If the charging communication does not work then it is a faulty fix from the techs and they don't understand how USB Type-C Power Delivery works and why it is possible that flipping a cable makes a difference. It makes a difference. \$\endgroup\$
    – Justme
    Sep 27, 2023 at 14:57
  • \$\begingroup\$ My working theory on their mystification is that most people who get it working great on one cable orientation would be happy to work with that, and never came back to complain to them about it. So they've never seen the issue when it came up before. I think a lot of consumers don't even realize its supposed to be a symmetric connector. \$\endgroup\$
    – T.E.D.
    Sep 27, 2023 at 15:23

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Yes the connector orientation does make a difference so it is a feasible fault mode that it works in one orientation and not on the other.

This is not unheard of even on non-faulty equipment that are just incorrectly designed and they work only when connector is flipped around to correct orientation.

Edit: As per my comment, this isn't about power supply pins, it's about communicating higher voltages for faster charging between devices.

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  • \$\begingroup\$ Thank you for taking the time to answer. So I take it that its not a typical design to charge devices using all power pins on both sides of the connector? \$\endgroup\$
    – T.E.D.
    Sep 27, 2023 at 15:24
  • \$\begingroup\$ @T.E.D. It's not about power pins. I said in my answer it's about communication pins. Now, in your case, I don't know what you are charging and with what charger, but both regular USB 2.0 data pins or USB Power Delivery could be used for communicating higher voltages for faster charging, and clearly the communication does not work properly if cable is flipped. \$\endgroup\$
    – Justme
    Sep 27, 2023 at 15:55
  • \$\begingroup\$ I'm confused. I'm not sure its vital to my question, but you're telling me the little USB wall bricks we plug our USB C cables into actually have communications logic in there going over the USB data pins, so in case they are talking to a USB C they can negotiate power levels? I'd assumed they were kind of dumb, since they theoretically can be used with any power cable that has USB on one end. \$\endgroup\$
    – T.E.D.
    Sep 27, 2023 at 16:08
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    \$\begingroup\$ @T.E.D. Yes. Either over the USB data pins or just over the CC pins, depending on which exact protocol or technology is used - PD or QC or whatever. They have to communicate to allow only 5V to old USB devices, e.g. 9V to your phone and 20V to your laptop. So, you assumed wrong. You don't need to know how they really work if you simply are interested to plug two things together and they just work. For designing such devices, there are standards that may span thousands of pages how it's really done and what the chips inside communicate. \$\endgroup\$
    – Justme
    Sep 27, 2023 at 16:13
  • \$\begingroup\$ Hmm. So that means this might also be why I can't get the wireless charger adapter I just bought to work with this device, no matter how much I fiddle with it. It works with my other mobile device (although its a massive PITA to find the sweet spot). \$\endgroup\$
    – T.E.D.
    Sep 27, 2023 at 18:47

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