Maybe a silly question but here goes:
My freetronics Etherten card.
The display I have just now says it doesn't work with the USB voltage and needs external power.
Terrific. The main board has a 2.1mm socket but nowhere does it say which is the + and -.
I'm guessing centre + but you know what thought did.
I don't want to plug it in and watch all the magic smoke escape.