When it goes down are you able to find your miners on your router or access the status page?
Which pool are use using and do you have back up pools entered?
Can you move one somewhere else in your house and give it a try? ( different power outlet and/or ethernet cable)
Do you have a volt meter to check the output volts under load coming out of the PSU? I have a couple cheap digital LED volt meter hooked up to both my PSUs and they show 12.2 and 12.3 on each S9.
Are your S9 the older ones that you can adjust the frequency or the newer ones that are auto? ( I have one of each and prefer the older ones.)
Are you showing the right hash rate for your miner when it is runnng?