I bought this from a Marketplace seller. It looked genuine at first. However, on closer examination recently, I found that this power supply was not quite identical to the original part: the label was not fixed squarely, the cable entry points were on opposite sides to the original parts and cable strain relief mouldings were not the same as the original. Once I opened the case to investigate further, I found that it was pretty horribly built inside. The mains power connector was barely soldered to the board! Mains voltage and low voltage parts of the circuit sat precariously side-by-side, sometimes only separated with adhesive tape. I would be not be confident using this charger after seeing the way it was built. There was no connection to mains earth, as there is in a genuine HP supply.
Even though I discovered this problem several months after purchase, Amazon provided an excellent resolution when the problem was reported, so 5 stars for Amazon's A to Z guarantee scheme.