I had some problem with breakers tripping. Then the source of the problem turned to be this extension cord made by Bachmann.
Sparking and blackening outside and also inside
It seems that child protection mechanism failed and part of it was stuck between contact bars. This then caused sparking on contacts, which caused blackening. End result was 10A breaker and ground fault protector to trip. This looked like a potential fire hazard, but fortunately the plastic material was not flammable.
Some deeper inspection showed that the child protection shutters were to blaim for the failure. Broken plastic part made a spring loose, and it caused the spring to make a short circuit. No winder that it tripped the fuse and made lots of black burn marks inside.
This felt quite good quality when I bought it, but after this issue this does not seen that good quality. They advertised that this is rewireable, but what does that help when the power jack part seemed to be the weakest link here.
It seems that while child protection shutters are a good idea to protect children, they can be in some cases be potential hazard sources itself (fire and short circuit hazards when they break).
Now this goes to trash..