How to test a fake/chinese iPhone Wall Charger?

Hi

i use to buy and sell iphones, many of them came whit no accesories at all, so i used to buy those fake chinese wall chargers for cheap, i was facing many issues lately whit those chargers, they do not charge on 3G iphones, or instead of charge it drains battery when connected, and cant charge 3GS or 4 Iphones.

But yesterday i plugged a beautifull iphone 3GS 16GB, and when connected to one of those chargers iPhone power off and never came back, i tried replacing the system board on a well know iphone parts and nothing, so board its kind of fried, i checked fuses and they seem to be ok.

Now, my question, its there any effective way to test those chargers, anything like an application on computer to test voltage and data- and data+ values from USB port ?

My multimeter always read 5.1V to 5.4V on chargers but the thing is how to test data from USB

Thank you all in advance.