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by hedora 978 days ago
That’s incorrect on all three counts.

Some “low wattage” specification USB-C devices are compliant with USB-C but are only compatible with USB-A power bricks because thet require 5V:

https://www.reddit.com/r/UsbCHardware/comments/c3q4s6/why_do...

Some USB-C cables are only 31 watts, and some devices can’t charge with less than 60W:

https://www.macworld.com/article/234030/how-to-tell-whether-...

Example brands from the above two links include JBL, Schooshe, and Apple.

I’ve hit similar problems with all my USB-C devices.

2 comments

> Some “low wattage” specification USB-C devices are compliant with USB-C but are only compatible with USB-A power bricks because thet require 5V:

This is because they are not USB-C compliant, despite physically featuring a USB-C port. The USB-C spec calls for any USB-C sink (i.e. device that consumes power) to include a pull-down resistor (Rd in the diagram on page 4: https://www.ti.com/lit/wp/slyy109b/slyy109b.pdf?ts=169690039...)

Devices that do not include this resistor, and are therefore unable to be powered with a USB-C to USB-C cable, are noncompliant and should not exist.

> Some USB-C cables are only 31 watts, and some devices can’t charge with less than 60W

As seen in [0], page 37, even USB 2.0 C-to-C cables will support USB-PD at 3A: https://host.zlsadesign.com/HJU_Drfba.png

The USB-PD handshake is performed independently of the cable, and uses the CC wire that is mandatory even in USB 2.0 C-to-C cables (page 76 of [0]): https://host.zlsadesign.com/Bk62vSMZp.png

You're right about the 60W point. Anecdotally, every device I've ever tried to charge has had no problems at 60W (although of course they'll charge more slowly than if they had 100W), but this is definitely not guaranteed.

0: https://www.usb.org/sites/default/files/USB%20Type-C%20Spec%...

And your Reddit link also has a comment suggesting using a USB A to USB C adapter. Those are also non compliant

https://hackaday.com/2022/12/27/all-about-usb-c-illegal-adap...

There is a certain combination of cable+adapter+device that can ruin your device. I don’t remember the details. I heard about it on the Accidental Tech Podcast