I originally deviated from my corsair cx500's that I used for the S1 and bought some sentry 750w due to the "4 pcie" but those POS won't even power one s3 when hashing starts (it powers off).  They would only power half the s3.   I am now powering my s3's with some cx500's.   My s1's have been running on the same supplies for months... Four are using cx430 which were slightly modified...