The XFX Pro Series 850W Black Edition easily complies with its 80Plus Gold efficiency certification when powered by either an 110VAC or 230VAC source. In the former case, the maximum efficiency reaches up to 91.6% under 50% load and a minimum of 89.4% under maximum load. If the source voltage is at 230VAC, the efficiency is boosted by about 1% across the entire load range, reaching up to 92.5% under 50% load and falling as low as 90.2% under maximum load.
Below 30% load, the cooling fan of the XFX Pro Series 850W Black Edition will not operate at all, which is why we have no reading below this point. At 30% load the fan starts and remains entirely quiet up to 40% load. At 50% load, the sound coming from the fan becomes discernable, even if only barely. If the load surpasses 70% however, the noise becomes clearly noticeable and the noise levels continue to rise as the load increases. However, such a load suggests that at least two powerful GFX cards are giving it their all, therefore it is unlikely for the user to notice the noise for the obvious reasons.
Despite the high power output, the efficiency of the XFX Pro Series 850W Black Edition is high enough to keep the energy losses low. As a result, we have a very cool-running power supply which can maintain very low operational temperatures, with the temperature delta being about 6 °C across most of the range and reaching up to 10.2 °C under maximum load.