tweet-a-watt require P3 kill-a-watt , but I already posse a very similar looks Japanese version
probably OEM? I opened up mine, it uses the same IC as P3 kill-a-watt for op amp. it would work , I am going to connect tweet-a-watt with this device.
the problem is that there is no room for xbee and a big capacita unlike in Kill-a-watt. I am going to piggy back it out side of the case.