I'm not sure. It's close to the limit.
If the PSU is not high quality then you may find it isn't safe.

I run the 741 on a 1250W OCZ Gold and the 721 on a 1200W Seasonic Platinum and I'm probably pushing them too hard but they are both quite high quality PSUs.
If I ever had the inclination, I could run the 741 using two OCZs since I have two, but for now I've left it on one.
The OCZ  is a very good PSU and I've had the two of them since I started GPU mining, without any problems.

The PSU that came with the Bitmain S2 was a POS, under powered, and died, but I've no idea what they sell now.