I'm trying to get an idea of how many pi's I can run at the same time from the same wall socket. I've done some research and it seems to me that the peak power consumption is somewhere around 750mA. If that is the case, then in theory 20 Pi's can be connected to one 20A circuit at my home with no problem. (I'm thinking about connecting them all via 2 10-port, externally powered USB hubs, if there's an issue there, let me know). I just wanted to run this configuration by some smarter, more experienced people when it comes to power requirements.
The instructions below Assume you mean 120volts at 20 amps which is the American standard. So we want to start by calculating the approximate wattage we could theoretically draw from the wall, which is volts x amps.
Now we are going to calculate the number of watts a Pi uses at peak load based on your research. We use 5 volts as that is the USB standard
Now all we need to do is subtract inefficiencies in the conversion from AC to DC which is approximately 10-20% for a good power supply, we will use 15% for our calculation. So now we multiply household wattage by efficiency(.85) to get the number of watts that are actually going to reach your Pi.
And now we decide this by the number of watts a Pi uses to see how many pi's we could theoretically connect.
There you have it 544 pis could be connected to a single 120 volt 20 amp outlet.