It turns out that you can’t trust any USB type A power adapter to be within spec.
I have a Catit Flower Fountain for my two adorable cats. The idea of a water fountain for cats may sound odd, but having one really helps with cats staying hydrated and that alone avoids all sorts of health issues.
At one point I wanted to see if I could create a sort of a DIY UPS for the water fountain. It would be quite bad if I was at work and a power outage results in cats not being able to drink water (they don’t really care for normal water bowls after getting the fountain). I had some battery banks available for testing, and I noticed that the pump for the water fountain is powered over a USB type A cable.
Should be easy, right?
Apparently not.
I tried multiple different power banks between the water fountain and the USB power adapter that came with it, and all of them would work for a bit and turn off after some time. I didn’t think much of it back then, but I did notice that two of the power banks I used started glitching out during normal use elsewhere.
Months later, I attached an IKEA power strip to the side of my work desk to make charging various things easier. It also has two USB type A ports and the water fountain was near the desk temporarily, so I plugged it in there. It worked, but I noticed that the water fountain was quieter now, the “hum” that it makes was almost gone. That made me curious, so I used the original adapter again and the “hum” was there again.
I took a look at the original power adapter specs to see if there’s a difference in the amount of current that these two different USB power sources provide. What I discovered instead was that the power adapter that comes with the fountain outputs a solid 7.5V. I measured the voltage with my multimeter as well, and it reports 7.71V. USB type A ports typically provide about 5V, with a maximum of 5.25V from my observations in the real world.
7.5V over USB type A is probably not safe with other devices, especially since a normal person only sees a USB port on the adapter and thinks that it is perfectly safe to use it to charge their phone or other devices. Yes, properly implemented USB type C ports can negotiate all sorts of voltages, but this is not one of them.
Probably explains why my power banks are acting odd now and glitching out.
This is why I have trust issues.
2023-12-19 update
By popular demand, here are the two adorable cats.
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