How can the unit draw 1Kw and only have a 1Kw PSU? This will not last long!!
Your 120/230V AC doesn't get converted to 12V by magic, there are losses and the power supply is rated to supply 1KW 12V DC at around 90% efficiency at high loads, I'll leave the math to you.
This was discussed at length earlier in this thread. Bitmain have checked with the PSU manufacturer that the load is within tolerance. Also, I believe the PSU is drawing 1,000W from the wall, not supplying 1,000W. It is probably supplying 900W to the miner.
TL;DR
Bitmain are professionals and know what they are doing with the PSU.