This is what I don't get either. I don't understand why people are not using the Bitmain APW3+++ power supplies. Yes you will be hashing a little less (in my case most of 13.5ths batches are hashing around 12.4-12.7 with extremely low hardware errors).
The answer is real simple. The APW3 puts only 1200w out when running on 110v. While your s9 may be running on that you are pushing the power supply dangerously hard and it will fail, if you are unlucky it will take out some of your s9 hardware with it. So dont be dumb and burn up your hardware because you dont understand how electricity and power supplies work.