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Comments on How interchangeable are USB-A power (charging) adapters?
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How interchangeable are USB-A power (charging) adapters?
As is typical, I have a bunch of devices that charge via USB and a bunch of power adapters to use with them. I've never been sure what's interchangeable with what, so I am careful to use the adapter that came with the device I'm charging. (Or, in the case of my most recent phone that didn't come with one, confirmed compatibility with the vendor.)
I have the impression I don't need to be this fussy. What information, from what's stamped on the adapter, is enough to tell me whether two adapters are interchangeable?
The proximate cause of this post is a USB-A adapter that has started overheating.[1] It says "output: 5V ⎓ 2A". Can I safely swap in any other charger that states the same output, or are there other factors I need to consider? This one also has an "efficiency level" that I don't know how to interpret (photo below). It's pretty old, so I'm mainly concerned about newer chargers being too powerful for what I'm going to plug into it.
I tried searching the web for the model number in hopes of finding more specs, but no luck. The device it came with is a battery/power bank made by a company that seems to no longer be in business.
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I'm assuming, since my house current hasn't changed, that this is a problem with the power adapter and not with the device being charged or the cable. If that's not a valid assumption, then perhaps I should be asking a different question. ↩︎
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If it plugs in, you can use it.
At least that's how it's supposed to work. Without doing anything, a device only gets a small amount of power at 5 V, assuming the host gives it any at all. That would make no sense for something like a charger.
The small initial current at 5 V is 100 mA if I remember right, which is only 500 mW. If a device wants more current, then it has to negotiate for it. The device and the host communicate to make sure what is ultimately settled on is within the capability of both devices.
It used to be that USB devices were limited to 500 mA at 5 V, so 2.5 W. Then charging options were added to the standard. These allow for both higher voltage and higher current, but only if both devices can handle it. My laptop, for example, came with a 65 W USB C charger. Since USB C is a standard, I can use any USB C charger that is rated for 65 W or more. The days of each laptop having its own proprietary charger are gone.
Again, this is how it's supposed to work. Your charger is rated for 5 V at 2 A, which is 10 W. It shouldn't be getting unusually hot when doing this, as it should be designed for that. If a device wants more than 10 W, then it should refuse the request during negotiation.
A properly designed charger should not let a device take more power than the charger can safely produce, and shouldn't get excessively warm in the process. Unfortunately, that doesn't prevent unscrupulous manufacturers and resellers from making and selling you products without proper protection and adherence to the standards. Scrupulous resellers don't carry chargers like this that aren't certified by UL or equivalent to be safe. I notice no such rating appears to be in your picture. If that's really true, toss it before it burns down your house. No, seriously.
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