There is a protocol to query/negotiate the available current on a USB port. Implementations handle this in various ways depending on what version of the USB standard they were aiming at and how closely they follow it. My guess is the negotiation doesn't work when the computer is off, so Sony doesn't charge at all but Unihertz makes do with some amperage that is assumed to be safe.

Are you referring to USB Power Delivery? If I'm not mistaken, didn't this protocol appear along with USB-C? Though not sure if this is even relevant, judging by a modern LED lamp I have (it works with computer off).

The lamp has USB-A on computer side (you can also use included power brick with USB-A port instead) and something non-USB on the lamp side. The lamp works when computer is turned off.

One more observation, the Sony comes with a power brick with USB-A port, but I keep the included cable plugged to the computer; on the odd occasion that I don't charge it on computer, I use charger of another older phone that I don't use anymore, Samsung Galaxy Mini from 2012. This charger's cable can't be separated, the brick goes to the power outlet, the cable baked into it leads to male Micro USB. Unsure if this brick has any brain (anything smart) inside.

If I recall correctly, doesn't plain old USB have voltage / amperage specified in the standard, something on the lower side, so one would assume any device providing power would output maximum specified in that standard. Maybe there's a difference in how much is output when computer is off vs on.

I've been wondering recently if power through USB port can be controlled through software on computer or at least if you can turn off the port completely, so eg. the lamp I have wouldn't light up. I admit, I don't know much about electricity.

https://superuser.com/questions/690074/what-i … t-of-a-usb-port