@TheAlmightyBaconLord @recoil44 thank you both for the motivation.
from my point of view, the arc / spark came from below the cap. That means that here is something conductive below it or that there is a sparkGap of probably a 1 cm.
1cm sparkgap means a pretty high voltage.
The Bang the spark made was seriously loud, and my right ear felt a bit of pain thrrough the rest of the day.
But the high-voltage idea is also controverse, because at some point it should have gone through the cap and not through the air between the pins.
The max voltage of the cap is probably lower then what it takes to bridge a cm of air.
The first "bang" incident wasn't that cap! And it blew the saftey which this time it didn't.
So i guess that its something else in the circuit and that just caused the spark at that cap.
Away from that topic though.
I am not willing to poke around and measure whats going on in the psu while its pluged in and hot / live.
I'd probably be dumb if i did!
Meaning that this will be a try and error game of desoldering a few parts, pluging it into the wall, probably getting deff from the bang, and then rense and repeate!
eat, sleep, rave, repeat
desolder, turn on, get deff, reapeat
disclaimer, i dislike the music.
The next steps that i will take:
Desolder stuff from the PCB to seperate the mains part from the rest. I don't want to damage that accedentaly.
And take of that cap with the hope that something is below it even though i doubt that!
Any ideas for after that?