I got my probe yesterday. I got the voltage and the positive/negative question answered. I hooked up an Alden female and ran some hene's with it today.
@ pseudolobster -- the square was indeed the negative
It is putting out 18KV. I forgot to mess with the pot to see what it might do. I haven't wired anything yet in a way that I can measure the current anyway.
If you recall, they sent me a second one (unsolicited --I had already left them positive feedback -- I told them, "Thank you.") because the key was broken off in shipment. I now have an extra. Does anybody need an 18KV brick power source that runs on 115V mains? You will have to change the wall plug, the Alden socket, and work with a key being broken off in the switch. The switch works, the key is just broken off in it. If you need/want it, it can be yours for $30 plus shipping.