* Sorry that this appeared in your feed. I didn't mean it. We just got the parts in mail so we should be getting some finalized schematics and designs up soon assuming everything goes well

The power supply is what is going to supply DC power to the electronics that are measuring and calculating the power. All of those 'wall warts' and cell phone charges are power supplies. Look around the house (or a friends') for one that says 5VDC on the label. Many cell phone chargers should work as well as some wall warts.

The power supply will have two main wires that we want to use. The +5V and the ground. You will want to determine which wire is which.

If you have a voltmeter, simply cut the power supply wire in half, strip the wires and then measure the voltage across them with it plugged in. Try to avoid letting the two exposed wires touch as it could ruin the power supply. If, when you measure the voltage, the display reads a positive rather than negative number, then the positive lead labeled on the meter is the positive lead on the power supply. Mark it so that you remember which is which.

If you do not have a voltmeter, check the label for a diagram showing how it is wired. This is going to be a difficult project for you with out a voltmeter, I recommend you get a hold of one.