Blown PSU

[maklabouhlel]

I recently plugged in a psu plug at the wall whilst the psu switch was in the "on" position and the psu went bang. Obviously I've learnt a lesson but I've been doing this for years and never had a problem. Why is the psu more prone to damage this way?

 

[maklabouhlel]

This youtuber did exactly the same thing and blew up his psu.