Indeed, at least I've added a fuse and Schottky diodes to protect the PC but I'd love some advises on how to be sure people won't fry their USB controllers :)

An isolating transformer, like the ADUM3160 ( http://www.analog.com/en/products/interface-isolation/isolat...) should be more than overkill in protecting there.

Interesting, thanks for the pointer !

I use an Olmex isolator [1], which I believe is also based on Analog's ADuM chip. Its worth knowing that the ADuM only supports USB "Full speed" mode (12Mbit/sec) and not the normal "High Speed" mode (480Mbit/sec).

[1] http://uk.farnell.com/olimex/usb-iso/usb-isolator-1000vdc-fo...

It's awesome that you made it all open source. You could probably spin up some kickstarter since making them in bulk would be cheaper (plus you get something for all the work you've done). I'd be happy to get one.

Resettable PTC fuse for overvoltage and P-Channel MOSFET for reverse voltage protection without a large voltage drop.

Yep. Although not related to this kit specifically, a friend of mine built a energy meter much like a kill-a-watt using a raspberry pi.

It plugged into 120 vac on one side, and usb to computer on the other side. He didn't end up doing enough to isolate the 120 vac side from the usb side and fried his computer. It was pretty impressive damage as it managed to fry the motherboard, CPU and memory.

haha nice :) I made wifi power meter using $15 chinese plug watt meter and ESP8266. No api no fancy stuff, just a webpage with three numbers.