A very handy pass-through USB device that displays voltage and current at the same time.
Techies often like to know what their devices are doing, and how well they're doing it. In the case of failing USB devices, it's nice to check if it's a power-related issue, and that's where this device really helps.
We've bought and played with several USB power meters in the past, and either they display power in strange LED displays, or alternate the display between voltage and current, but the KCX-017 displays both at the same time, and also sums up the consumed power in up to 10 selectable memory slots. These memory slots are useful for comparing the true power capacity of portable USB power banks.
We often compare different USB cables for charging our phones with this meter, and there's a surprising difference between available cables. You can't see the wire gauge in a USB cable, but this tool definitely lets you make an good guess at which ones use bigger wires in the cable. This also makes it ideal for diagnosing strange reboot failures in Raspberry Pi SBC-style computers (beware the Raspi flashing rainbow icon, which signifies low power!).
A very handy feature is the micro-USB input, which allows you to plug any micro-USB power supply into the meter instead of using the provided standard rectangular USB type-A plug. We often use this feature for checking the rated power output of a USB wall-wart cellphone charger.