I have same problem with an Acer Notebook (Aspire E5-575G from around 2016). During normal usage it instantly went completely OFF and never came back. Tried all version of cable-plug-in-out/power-button/battery-disconnect etc.
If I plug-in the power cable, the orange/blue LED are lighting and thus indicating battery is charging/full and mainboard is correctly powered. But if I now press the POWER Button the LED is flickering (gets a little bit darker, went off, and comes back within about 2 seconds). For me it seems as there is any short circuit / overload present on mainboard.
I opend the notebook and searched the mainboard for any obviously demages (died ELKOS, resistors etc), but could not see anything (but it is hard to distinguish). Made the above test with opened mainboard again: during this 2 seconds-LED-flickering-after-power-button-is-pressed I can hear a very silent noice/squeeze coming maybe from nearby the DIMM/RAM banks. PLUS: I noticed, that a certain component gets very hot, which in my eyes shold not happen. I marked this component on the picture (see below), labeled with “2R2 628 E47”. I guess it is an resistor? And I guess just changing this is most likely not the to solve the root cause. Anybody does know it better?
Maybe the most important point: the failure just happens 2 days after I had to use the notebook with an non-original power supply - and I guess this was the cause of failure. It was an older universal power supply with 100W and a voltage switch (12-24V, I of course just used the 19V setting, but maybe it is malfunctioning or have a bad DC signal…).
So bottom line: just use appropriate voltage supplies for your notebooks ;-)
For sake of completeness: I also changed CMOS/RTC battery (CR2032, 3V), but no change.
I think I will give up - and order a identical, used Notebook and will “just” switch my SSD.