I was previously using a Chinese generic USB charger, but didn't much like the build quality of it. I then started researching USB chargers and decided it definitely needed replacing, in particular after reading a USB chargers review on a blog by Ken Shirriff: generic chargers have low efficiency and poor power quality, the worst are unsafe to use. The HP charger was top rated in that review.
Now, this charger: part is P/N 157-10157-00. This is a 2 amp charger. I bought from seller Luzern and did get this part. In the past I believe some other sellers have sold other HP chargers that are different part numbers and only 1 Amp rating under this product, hence some negative reviews of this charger.
What's good about this charger: high build quality, kit comes with AU, EU, UK, US adapters (4 heads and barrel twists off to keep charger small to carry around), also comes with a micro USB cable. I have used this to charge an HTC phone with no problems. Details on power quality, efficiency etc.: see Ken Shirriff's blog post.