Technical question bout internal fuse or capacitor damage on iPhone 4s

A couple of days ago I charged my iphone with the original usb adapter to the wall plug, in the right moment when I plugged the phone it came a little spark from the wall plug then my iphone was shut down by itself .

I tried to turn it on normally but the phone did not responde, so I did a hard reset holding power and home buttons after that the phone is working properly.

Usually now I have been charging the battery in the same electric wall plug with the same usb adapter and also with my laptop.

So my question is what happened that day? why my iphone was shut down by itself and later everything just work correctly, I know that electronic devices are protected with fuses or capacitors, but also I know that USB adapters come with such protection to protect electronic devices.

Even my phone works correctly do you think some fuse or capacitor has been broken that day in my iphone?, I dont think it was a shortcircuit because the fuses and the electrical installation of my house are intact, the electrical plug and my usb adapter both also are intact, I would appreciate any information about this guys.