Power adapter plug became black at the top

[Pharetra]

I just saw that the plug of the adapter of my sister's laptop is a bit black at the top and it doesn't feel as smooth as I'd expected. Is that normal? I think it's just a sign of it being used and it still works, but I'd rather be safe than sorry when it comes to this stuff

I've got some pictures here:
https/drive.google.com/open?id=0BxRHkrPe5ANuTy1oWERLd2JKVFk
https/drive.google.com/open?id=0BxRHkrPe5ANuWks2clQ1RElxY1U

 

[Ironsounds]

Hello... Yes... Great pics... This is an example of Electrical contact "PITTING" There is a worn out, poor mating, between both sides of the connection. The electrons are being confined to a small contact area of the metals... causing over temperature and melting spots.

You should replace both sides of the connection devices. B /