Try Usb ports on your computer, charging cables, chargers you have.
The USB tester device will show you on the screen of the voltage and current.
Does not normally charge your mobile or your tablet?
Does the charging cable that you are not of good quality or is worn or damaged;
The trend that puts your computer or your charger is very low;
All this and much more will answer the voltage measuring device and USB power.
Simply plug in the USB port is taken, connect a device to output and will give you measurements for voltage and current accurately.
Current (0-3A) can detect mobile phone charger voltage compliance DC5V
Voltage / Current: 3 ~ 7.5V / I = 0 ~ 3A
Error: voltage <± 1% current <± 2%
Full scale drop: When (measuring current 200mV)
Operating temperature: 0-60 ℃