Hi,
Regarding your title "Only while plugged in, the Laptop screen(goes black)"
Is it the power adapter the issue or maybe the power management settings?
I've changed the power adapter and there was no chng. Recently I forced installed Intel MEI ver 9.5 driver through device mgr because the setup stopped me saying the laptop isn't compatible. So the sleep issue which I had, is now resolved(all issues I had before actually are fixed) but one last thing remains i.e., if i leave my laptop idle while plugged and the screen after display time out doesn't wake. So I've changed the power settings to never and turned on screen saver, that was temporary fix for me.
I think this is because of buggy bios update itself now cause I've tried everything and nothings left, and this started after that update so I'll just wait until nxt update hope it'll fix this one last issue.