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Comment by raybb | Hacker News Reader

Back in 2019 I went on a search for an electric toothbrush with a usb-c charging port. I found one that seemed reasonable and it was from Xiaomi. I've quite enjoyed their phones so gave it a shot and have been pretty happy with it since then. Only downside is that it doesn't charge at all using a macbook charger. I guess it might be due to too much power? Using smaller charging bricks seems to fix it.

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Part of the modern USB PD spec is that the two sides of the negotiation usually have a set of voltage/amperage pairings that they'll do (the highest aggregate pair(s) giving you the wattage of the adapter). Sometimes the things won't find a configuration that matches and so it won't charge. That's why, for eg., you can't charge the Nintendo Switch Dock with a macbook charger but can charge the switch itself. The dock is really picky (basically only does the pair the official nintendo adapter wants) and so is the macbook charger. The switch itself is more flexible though.

That said I would have thought the toothbrush would just do normal old USB charging, and that should work on a macbook charger no matter what I'm pretty sure? But maybe not.

Edit to add note: I think the most commonly missing voltage is 12v, so your toothbrush might want that.

The Nintendo Switch Dock wants 2.6A at 15V, so it doesn't work with the 30W Macbook Air charger which provides a max of 2A at 15V. The higher powered Macbook chargers work just fine with the Switch Dock.

Higher wattage chargers do not provide more power than the device being charged draws. Try reversing the USB-C connector, with some devices I have found that the reversible connector is in fact not always reversible.

My vape refuses to charge with a high wattage charger. Reversing doesn't work.

Likely not caused by the fact that the charger is high wattage.

I have an Anker charger with two ports which use different tech to detect what the device needs : an USB A with Anker's poweriq (which supports multiple fast charging standards like qualcomm QC, but it also charges devices that don't use fast charging), and an USB C port that only does USB PD.

My vape only charges on the USB A port with poweriq. The strictly USB PD port doesn't work for it (but works on all my other devices).

I've decided in the future I will only buy chargers from Anker that have their proprietary poweriq thing, and dismiss anything that only supports USB PD. Poweriq 3 also works with USB PD devices so having a charger or a port that only does USB PD seems useless.

My PS5 DualSense controller will not charge from my 45W / 60W USB-PD chargers, but will charge from the USB port on the PlayStation, or a USB port on a computer.

tbf, sony controllers have always been really finicky about what they're attached to in order to be charged. I can never figure out what's up with my DualShocks 3 and 4.

It's nothing to do with the higher wattage, but they didn't Xiaomi implement USB PD up to spec. Likely missing the pulldown resistors on the CC lines.

You can read more about how they should implemented the PD sink here: https://medium.com/@leung.benson/how-to-design-a-proper-usb-...

I wish the standard had included something on the cable and PD port to signify how much power they were capable of handling. Something like 3 little LEDs (one for less than 50W, two for 50W-100W, etc or something) or even just a number like 50W, 100W, etc. The user experience so far is kinda scary levels of vague.

I have commented it before if the inside of then were color coded like USB 3 is usually blue.

The problem ist that USB-PD allows a lot of different voltages, and chargers have a different max current for each voltage. Many newer chargers are even programmable, where the source can request arbitrary voltages and currents.

Power supplies typically have supported voltages and currents printed on them, but in my experience the easiest way to figure out if it works is to just try it.

I think fixed-voltage chargers are supposed to all do 3 amps max for any voltage below their top voltage. If that's wrong let me know.

I don't know what the rules are for programmable supplies.

That's not correct. A 30W charger might support 3A at 5V and 9V, but only 2A at 15V and only 1.5A at 20V.

You're right. I had it a bit wrong.

What I should have said is if 3A at a standard voltage is within the charger's watt rating, then the charger has to support at least 3A at that voltage.

A charger has a top mandated voltage that depends on its watts. Standard voltages below the top mandated voltage, which is 15V on a 30W charger, have to support 3A.

But chargers are allowed to offer higher voltages if they want to. Thank you for clarifying that.

(And I did check the spec for this post, it is mandatory, USB Power Delivery Specification Revision 2.0 Version 1.3, section 10.2.2, Normative Voltages and Currents.)

Edit: I also checked the programmable supply rules now in Revision 3.1, it looks like 1) they have the same math mandating at least 5/9/15/20 volts based on wattage, 2) you can choose any voltage between 3.3v and the mandated max, 3) at those voltages it has to supply at least min(3A, [supply wattage] ÷ [chosen voltage])

Seems like they should have just standardized one (Volts, Amps) tuple so you can at least always charge, even if slow. Like the (5V, 0.5A) we had...

5V 0.5A is always available. But the higher voltages need to be negotiated, and some devices need more than 5V to work.

I found this comment about electric toothbrush interesting.

https://news.ycombinator.com/item?id=29359544

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