Just a little post in case anyone is interested. The Ted 5000 monitors power coming in to your home via both phase wires. It comes with a web server which you can easily point Mango to and exact values from the device.

I created a data source of a HTTP Retriever, then set the URL to http://ted5000/api/LiveData.xml. You can set the update period to whatever you want.

You can then add your points. Here is an example:
To monitor the current power draw:
Data Type: Numeric
Value RegEx: <CostNow>(.*?)</CostNow>

That should do it!