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.

Tux and Põssa. Põssa can be roughly translated to "Piggy" in English. I'll let you guess how he got that name.
Tux and Põssa. Põssa can be roughly translated to "Piggy" in English. I'll let you guess how he got that name.


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