What exactly does overheating mean? Does it feel hot when you touch it? Is it hot to the point where it is painful to touch? Is there smoke or burn marks? Various "wall wart" kind of devices can get up to some 70-80°C without that necessarily meaning any malfunction, as they will have heat sinks internally. If it gets too hot to even touch or smoking/burning, then the most likely culprit is IMO a blown protection diode, which when it blows leaves a short between supply and ground, causing a lot of heat but not necessarily affecting the functionality otherwise. This can happen if you had a lightning strike nearby when it was plugged in, for example. If so then you shouldn't be using it as it might have turned into a fire hazard (the fuses in your house might hopefully blow before it comes to that).

Very hot to the touch (I dropped it on something fireproof quickly), no burn marks or smoke or redness on my hand later. I can't think of anything unusual in its recent history, like being plugged in during a storm. No problems with anything else plugged into that wall outlet before or since. (The charger stays on a shelf between uses; it's not permanently connected.)

Monica Cellio‭ Ok so probably it's just some other component that has broken for whatever reason - the low quality product theory. USB devices from China are kind of notorious for this.

(Anecdote: I had a brand new USB port extension card in my PC that spontaneously combusted without provocation - suddenly there was smoke coming out of the PC. Some reverse-engineering revealed there was an internal short between 5V and chassis caused by a slightly bent USB-A connector. The short caused some ferrites to burn up. So I actually repaired it, but the cause was low-quality components in combination with no quality testing after production.)