iPhone adapter wall socket blew up!

My grandson gave me his old iPhone 4S to use plus adapter which, he bought from amazon as a genuine product (I know what you are thinking!) he told me it needed fully charging up. This I did when I got home plugging it into a wall socket low on the wall in my kitchen near to my dining table. I kept checking how it was getting on but it did not appear to be doing much. After about 2hrs I sat at the table to do some work, checked again, still no improvement when all of a sudden the plug exploded, very very loud bang, shooting the front part and the inners right past my leg (thank goodness the socket was not head height, makes me shiver to think what might have happened). The back of the adapter with the pins is stuck in the socket, black inside the plug and around the socket and the phone lead shot out of the adapter.

I thought it had fried the phone but after I had gotten over my fright (well I am 66!) decided to try to charge it up with my ipad2 adapter as there appeared to life left in the phone! This worked perfectly. Since this has happened I have checked the internet and it would appear that Apple were replacing some of these adapters last year at a reduced price if they were taken into one of their shops.

I do not have a shop near me and I cannot find a correct telephone number (uk) to ring about this as it feel someone should be advised. My grandson has now gone back to university a long way from me as I am sure he would have helped me with this.

Would be grateful for any help. Is it still ok to charge the phone with the ipad2 adapter?

I have taken photographs.