Screen goes black sporadically - Notebook?

I have an unusual phenomenon that I need your help with.

I will now ask the question without any technical information:

I connect my notebook to a monitor with an HDMI cable. If the notebook is NOT connected to the power supply, everything works fine. As soon as I connect it to the power supply, the image on the screen sporadically goes black for 1 to 2 seconds and then comes back. As I said, the effect only occurs with power supply.

The following tests have already been carried out by me:

Another HDMI cable used
other monitor used
other circuit used
tried another power supply
Graphics card driver completely uninstalled and reinstalled
Energy saving settings adjusted

Unfortunately, all attempts lead to the same negative result, so I'm at the end of my game.

This effect prevents frustration-free work on the notebook or on the screen.

I hope that someone still knows a further solution and the problem can (finally) be fixed.

Which GPU (graphics chip) does your notebook have?

Please try to match the Hz number on the external monitor to your notebook's TFT or, if necessary, to set it differently.

It is often the case that the Hz setting causes this problem (but this is in contradiction to operation with a power supply unit)

That is just because of the electricity.

It can happen that the power supply affects other devices on the PC.

I once experienced the following, whenever I used a lamp that was only connected to the same socket, my PC made the USB sound as if something was plugged in.

So you see electricity has very interesting connections.

Strange phenomenon, but quite true and a good approach.

It was probably just because more electricity was used from the socket, and my PC got very small millimeters less in the second it was switched on or off.

NVIDIA GeForce GTX970M, I have now adjusted the Hz number, 59 Hz were previously set, I switched it to 60 Hz and will continue to monitor the situation today.

Type on it you have 2 graphics cards in the notebook NEN intel adapter and a nvidia or something

In this case it switches to the nvidia at full speed in the network mode and this causes this short dropout!

However, the dropout is not a one-off; it also occurs during ongoing operations

So I observed the facts, unfortunately the same effect again. It has something to do with the power supply to the power supply unit, since, as already described above, the effect does not occur with battery operation.

Does that also happen when the battery is at 100% and then the power supply unit is on?

Yes, the effect also occurs with 100% battery. I have already removed the battery, but unfortunately it doesn't change anything

But also if the effect occurs in 3 different places (i.e. Another building)?

Doesn't change anything about the power supply.

But still strange that only happens with a connected power supply and no matter which monitor…

No, if the power supply has a way, that's no wonder.

I bought a new power supply → same effect

Probably had to go to a professional if it doesn't get better.