I bought this USB meter, along with This other quoted in this article to know what the voltage and current of my sources and USBs. There is a huge variation, and that explains why the devices do not carry in some places, What can be the fault of the cable or the source.
USB gauges are similar, have an entry to connect to the source computer and USB or a USB output to connect the device that you want to load. The meter is on the way, between the USB and the device under load.
This meter there is a button that switches the display, showing other information. The interesting part of the meter is that it can be connected in any way to any USB!
When you turn the meter on USB, and does not connect anything in the output, He simply shows the voltage of 5V. In my case, 5.16V (about 5 ~ 10% is tolerable).
When you connect the phone to load, the meter shows the 0.45 and the voltage drops a little. The load will be slow, because my phone loads the source with almost current 1A.
See a tablet connected to the meter, the chain is 0.71 to, which would not be possible in a computer USB (500mA Max.).
There are three different types of display: in one of them appears the USB voltage and charge current. Also the power, the time that is under load and the amount of charge information on Ah and Wh energy.
In another screen we have the tensions of four wires of the USB, Obviously in relation to the V- (Why is 0V). We have the electric resistance equivalent of connected device, the temperature and anything else you can't figure out what is.
In this display we have the current, the device's battery capacity in mAh (have to leave loading 0 to 100% to register correctly) and another half a dozen less relevant information:
Also a USB cable Extender to connect directly to the source:
Pretty cool the meter, and the results seem reasonable. Those interested, You can take a look at Banggood where I bought the product. I leave also link to the other cited in the text: