In an earlier post you stated that you are not an electrician. That doesn't mean that you can't start trying to think like one. That means trying to err on the side of "more than adequate" power supply for each of your miners. I wouldn't be thinking: "What is the maximum number of things I can get away with connecting to this PSU, including my brand new Antminer S3". I would be more like: "I will be using 1 good quality PSU to power my new Antminer S3, and that PSU will not be supplying power to anything else."
And i would say good luck to you....
I have an S1 & an S3 connected to the same power supply, Works no problems... My rig's aren't overclocked so no dramas...
If S1 Push = 400w & S3 Push less than 400w then a 1200w power supply is fine...
I'd even go as far to say that a corsair 1000w power supply has all the modular plugs u need to run 2 x S3's off without a trouble in the world.