I bought this charger as a spare to keep in the office in case I needed to charge my phone during the day. It seems to work ok - it certainly charges my phone - but it charges it much, much more slowly than the original that I keep at home. For example, this morning it has taken more than 3 hours to charge from 17% to 67% with the phone not being used at all during that time. So, although the markings on the side of the charger suggest that it's identical to my original, I'm really not convinced that it's a genuine Samsung charger.
Updated 4 December 2013 - This charger, which I bought from MOBILE NEEDS is absolute rubbish. I've only used it 2 or 3 times and it doesn't charge my phone at all now. Definitely not the genuine article so don't waste your money on it.