The USB-Bug will dTest Power (0 to 99.9W), Voltage (3.2 to 30VDC) and Current (0 to 3A) on USB 2.0 and USB 3.0 charging ports with over-voltage, under-voltage and over-current indicators
Measure capacity (in mAh) to verify output of portable battery pack
Intelligent charging feature automatically selects the safest maximum current for your phone or tablet (charging your phone or tablet up to 50% faster)
Dual output for charging two USB devices off of one USB 3.0 port; One port is a specially designed masked port to charge your phone or tablet without any data being transferred

Triplett USB Power Monitor