I feel that Bitmain is skimping on the PSU.  Assuming that they're using Enermax ERV1000EWT-G 80 Plus Gold which is approximately 90% efficient at around full load (996W or 83A total on the 12V rail), the S2 would be drawing around 900WDC (1000WAC at the wall*90%) from this PSU.  That's a 90% (900W/996W) continuous load 24/7.  That's too close for comfort.  A 1200W PSU (75% load) would be more appropriate.