I've got a raspberry pi 3b+ mounted in my wall with the [official 7″ touchscreen](https://www.raspberrypi.org/products/raspberry-pi-touch-display/), and after some time i noticed the symbol in the top right corner notifying that it does not get the voltage it's supposed to have.

I'm powering it with a [switched powersupply](https://www.kjell.com/se/.mvc/Document/File?id=a191b3e4-6e01-4025-b1d3-aac800ef586e) that is rated for 50W(5VDC) which should be plenty enough. I took a measurement with my multimeter and it was reading ~0.800A the pi is connected via the pin header. When i instead connect this with a mobile adapter 4A, i don't seem to get the low voltage notification.

I can recall that i a while ago accidentally connected the pi with reverse polarity, this was less than 1s it still boots up fine can this be the reason or do you think this can be caused by the power supply being faulty or doesn't recieve enough load?

Is there a practical way of putting load on the PSU to see if it's capable of drawing more than 0.8A?

Edit:
One thing that is relevant that i forgot to add is that i tested the voltage given by the power supply and got a reading of 5.1V