Emsa wrote:It seems it's definitly the case of more voltage being needed. Tried to compile one emulator from source and during the compilation the low-power symbol is on all the time (yellow square). And that's on default clocks and over voltage 6!
There are two different warnings. According to this post
a red square is for over-temperature
and a rainbow colored square is for under-voltage.
Assuming that it is the symbol for under-voltage: The low power symbol is a different issue from the processor not being stable without adding more voltage in config.txt, and it is not cured with more voltage to the CPU. (You did not mention the low power warnings in your previous posts so I assumed that you did not get them at least with your first Pi3 and power supply.)
The problem is that your power supply drops the voltage it gives to the board when it is under load. Probably all PSUs do this to some extent, but when the Pi receives less than 4.65V it shows that symbol. It is a bit odd that that happens with the official PSU, but there have been previous reports of that also.
In this case the problem should be cured with more voltage to the whole board, and not by modifyinf config.txt. If your power supply got a fixed (permanent) cord (the one connecting the PUS to the Pi) there is nothing you can do about it on the power supply side. If it has a changeable USB cable, try a different cable. (Shorter cables are usually better than long ones.) On the side of the Pi: What do you have connected to your Pi? If you have something connected that needs lots of power, changing that to something less power hungry might be the solution. In the Pi itself, you could instead of adding voltage - and adding more load for the PSU - lower the CPU frequency, i.e. underclock your Pi. Of course, you could try with different PSUs, if you got some with enough amperage, and see if any of them fares any better.
In the case of over-temperature warnings: get a heat sink and use a well ventilated case.