Regarding #2, it would be better to have the plugs be like that of earphones; one big hole (to accommodate the extra power ofc) and have the end be one electrode, the middle be another, and the top be the grounding (or some combination). Actually, it's exactly like the 12v 'cigarette' car plugs. Just smaller.
I think you mean three. Hot, neutral and ground. If your circuit is completed with the hot and the ground, there's a major problem in the wiring.
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Now, with that said, a round omnidirectional socket could still be accomplished with a ground stud in the middle and the two poles around the outside. The contacts would need to be set up like the contact points on a Variac.
http://en.m.wikipedia.org/wiki/Autotransformer
Everyone should own those things
Here's an example: http://www.harborfreight.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/i/m/image_18165.jpg
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Now, with that said, a round omnidirectional socket could still be accomplished with a ground stud in the middle and the two poles around the outside. The contacts would need to be set up like the contact points on a Variac.
http://en.m.wikipedia.org/wiki/Autotransformer