I have a Corsair AX1200 high end power supply having min 90% efficiency at 50% load.
I loaded it with an overclocked S3 (s) running at 250Mhz and 500Ghs+.
The power consumption at Wall is around 400W at 220VAC.
I then connected it to a 12V DC Source directly omitting the Power Supply.
Now the power consumption is around 260Watts to 300Watts, the DC-DC converter's efficiency is near 90%.
So, I should assume from my findings that before PSU the S3 consumes <300Watts and at all 430W.
The ammeter used in both case where same and did testing multiple times with same results.
Antminer S3 <- 24VDC-12VDC Converter <- 24VDC Solar Charge Controller <-  <300W
Antminer S3 <- Power Supply                <- 24VDC Invertered to AC         <- 24VDC Solar Charge Controller <-    430W