So a few months ago, I stumbled upon a thing at Adafruit.com called a "Charger Doctor" which was really just a Multimeter designed to slip inline with your USB cable. It was $7.50 and I liked it.

While using a digital multimeter to diagnose electrical problems on customers’ equipment, I frequently hear the comment, “I’ve got one of those multimeter things, but I never learned how to use it.” ...

Fluke Corp. has introduced a new, easy-to-use utility multimeter designed to help utility workers, linemen and electricians, to quickly diagnose electrical problems. The Fluke 113 Utility Multimeter ...