Just got the DROK USB test dongle, and I LOVE it. Instantly shows me actual voltage and current draw to easily analyze USB chargers and cables. This is much more accurate compared to something like Ampere, or any other app really, and removes software from the equation when testing multiple devices.
Under $15 here: http://amzn.to/1BHODma
The reason I went with that one is it supports up to 13V, meaning even the QC2.0 12V variety (let alone 9V). Pretty future-proof stuff, at least for now.+David Ruddock
got the same one and is working on a piece for +Android Police
talking about it.
I'll be playing with it more in the coming days to see just how good/bad chargers and cables can get.