I have a Raspberry Pi 3B+, running Raspbian.
Linux raspberrypi 4.19.97-v7+ #1294 SMP Thu Jan 30 13:15:58 GMT 2020 armv7l GNU/Linux
It server primarily as a MagicMirror2 machine.
I can see the little yellow lightning symbol on the screen always, it flickers a few times during boot, but then practically stays on the whole time. The RPi is connected to a 60W, 6-port USB PSU. (2x 2.4A, 2x2A, 2x1.4A ports, RPi is on one of the 2.4A ports).
I initially though it was a case of bad power supply and decided to order a new one, but while waiting for the new PSU to arrive I decided to test it with an inline USB voltage/amp meter.
The meter reports the RPi is drawing anywhere from 0.64 to 0.88 amps (EDIT: was "watts", my bad) of power and the PSU is supplying it with 5.13 to 5.16 volts.
Surely that isn't supposed to trigger a low voltage signal at all, let alone be constantly on?
ps. there is nothing connected to the Pi other than a regular PC monitor, not even keyboard and/or mouse.