Huntkey decided to use a very unique design on the X7 900 W power supply, with an interleaved active PFC circuit and phase-shift full-bridge switching circuit. This is the first time we’ve seen a PC power supply using such designs.
Noise and ripple levels were extremely low, and voltages were almost always closer to their nominal value. We were, however, a little disappointed with the efficiency results. Efficiency was between 87% and 89% when we pulled between 20% and 60% of the power supply labeled wattage (i.e., between 180 W and 540 W). When we pulled 80% of the labeled wattage (i.e., 720 W), efficiency dropped to 85.5%, still a good number for most users, but this is what the unit should provide while delivering 900 W. At full load, efficiency dropped to 81.8%, a number that is below the minimum required for the 80 Plus Bronze certification (keep in mind that this unit is officially an 80 Plus Silver one).
The main reason that made efficiency fall below 85% at full load on our test was the AC voltage. The voltage in our lab is 115 V, but as we increased the power we were pulling from the unit, the AC voltage decreased, as you can see in the results table. An AC voltage below the expected value makes efficiency drop. We didn’t use any voltage stabilizer to keep the AC voltage constant because we wanted to see how the tested power supply behaves in a real-world scenario.
Remember that our tests are far more rigorous that those conducted during the 80 Plus certification. We test power supplies between 45° C and 50° C, while the 80 Plus tests are conducted at 23° C, a temperature that makes efficiency higher than in real-world conditions. Also, we try to pull as much current/power as possible from the +12 V outputs, as this reflects the usage of a modern PC. With a load configuration different from the one we use, efficiency numbers may be different.
We were also a bit disappointed with the relatively reduced number of SATA power connectors (six). We think a 900 W unit deserves at least nine of them. On the other hand, the X7 900 W provides six connectors for video cards, supporting, out of the box, three-way SLI and CrossFireX configurations.