I am in process making Raspberry Pi 3B my primary development system.
I am experimenting with adding USB devices, with some success. With several USB device connected via EXTERNALLY powered USB hub I have some minor issues with them, but NO POWER issue as far as I can tell.
BUT after going back to minimal configuration - only USB wireless adaptor connected - I started getting this lightning bolt ALMOST every time the monitor changes. ( No , changing the monitor intensity IS NOT an option , I am looking for an answer , not "try this " band-aid) The power indicator red LED stays on full time and I am still using SAME main power supply.
It sure looks as the monitor "power" also runs FROM USB devices and NOT only from the main power.
This is not a big issue, since it works fine when / with externally powered USB hub I'll be using anyway. I just like to have some clarification why is this happening on "bare bones" Pi.
Please , no "use official power supply by...." , I appreciate if you read the post before replying canned way and not waste your and mine time.