Yeah, Nvidia actually recommends a min 850 watts power supply unit, just to be on a safer side, but you are already having a high quality PSU, which should be enough despite it being below the recommended specs.
I mean, PSU's WATTAGE alone doesn't always matter that much, because the QUALITY of the PSU is what one should be looking for mainly, quality of the components used/CAPS, as well as the total AMP drawn on the +12V RAIL (output), the efficiency under load, "ripple suppression", among other factors.
The OEM also matters a lot, instead of the actual PSU brand. I've seen PSUs labelled as 1K watts, but in actual real world scenarios, they can hardly pull 400 Watts from the wall, even under full load.
I presume your PSUI is Platinum certified as well ? Anyway, the Focus PX is a reputed lineup of PSUs. You are good to go.