I read a similar writeup for USB power adapters and headphones. I'll see if I can find it, but in short, I will never buy a cheap USB power adapter. You're just asking to have your iDevice fried.

Here's one: http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-apple-is.html

Just... just scary. Sometimes it pays to buy name brand. Looks like HP has a really good charger.