Why does my screen flicker when it's plugged in?

@mikejones61665 you are not telling us if the screen flickers when you are not using the AC adapter. If it only flickers when the AC adapter is plugged in thatn there are commonly two issue. One being that the AC Adapter is the problem. It does more then just converting the voltage to something that your laptop can use. It also converts AC wall power to smooth DC power. If the filter capacitors inside that adapter are failing, it will send fluctuating power (AC ripple) straight into the logic board. The motherboard can't regulate that ripple and the voltage fluctuation bleeds directly into the screen's backlight power rail, causing a visible flicker. A oscilloscope would prove this but you can test it by using another known-good charger see if that eliminated the flicker. Also, plug it directly into a wall outlet, bypassing any power strips, to rule out a bad ground.

If a new charger does not fix it, it is possible that the issue is on the motherboard. There is a power management circuit right behind the DC-in jack that handles switching the load between the battery and the wall power. If a MOSFET or a capacitor in that specific circuit is failing, it will drop voltage to the eDP display connector every time it tries to charge the battery and run the laptop at the same time.you would need to do a visual inspection of the motherboard and check the charging circuit. To help you with that, we would need to A. know what motherboard you compute is using. It'll be printed on the board. B. we would need to see your motherboard. Post some well focused images (both sides) of it with your Question. Adding images to an existing question

Now, if your screen flickers all the time (with/without AC adapter plugged in), then we are looking at different issue. Let us now what you find out.