If you like to tinker with your own electronics projects or are a data geek who needs to know how much juice your tablet, smartphone or other USB device really needs to charge via USB, the Smartronix USB Power Meter will provide that info. It can also tell you how much power a USB port can provide. The built in LCD displays the USB port’s precise voltage (between -19.99V and +19.99V) and the exact current flow (up to 1,999mA). The USB Power Meter runs on 2 AA batteries and is available from CyberGuys for $49.95.
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Neat product. Beats hacking up a USB cable and trying to wire in a multimeter. Seems like half the big USB external drives exceed max USB power these days. With this I can be sure.
Looks nice, but I found another much better choice for USB Power Meter – a low cost LED based USB voltage and current tester from amazon website http://www.amazon.com/AboveTEK-Charging-Monitor–Multimeter-showing/dp/B00HTAH3KY/ie=UTF8?m=A37ZOD60SUJEE6&keywords=usb+power+meter , same function and feature but less than 10 bucks.