As one would expect in a high-efficiency power supply, the XFX PRO 850 W Black Edition Full Modular uses a synchronous design, where the Schottky rectifiers are replaced with MOSFETs. Also, the reviewed product uses a DC-DC design in its secondary. This means that the power supply is basically a +12 V unit, with the +5 V and +3.3 V outputs produced by two smaller power supplies connected to the main +12 V rail. Both designs are used to increase efficiency.
The +12 V output uses four PSMN2R6-40YS MOSFETs, each one supporting up to 100 A at 100° C in continuous mode, or up to 651 A at 25° C in pulse mode, with a maximum RDS(on) of 3.7 mΩ. This is the same configuration used in the 750 W version of this power supply and in the Corsair AX760. The Seasonic X-Series KM3 650 W uses only two of these transistors.
As explained, the +5 V and +3.3 V outputs are produced by two DC-DC converters, which are located on the same printed circuit board as the modular cabling system. The two converters are controlled by the same PWM controller, an APW7159, and each output makes use of three BSC0906NS MOSFETs, each one supporting up to 63 A at 25° C or 50 A at 100° C in continuous mode and up to 252 A at 25° C in pulse mode, with a maximum RDS(on) of 4.5 mΩ. This is exactly the same configuration used in the XFX’s 750 W version, in the Corsair AX760, and in the Seasonic X-Series KM3 650 W.
The outputs of the power supply are monitored by a WT7527 integrated circuit, which supports over voltage (OVP), under voltage (UVP), and over current (OCP) protections. There are four OCP channels, one for +3.3 V, one for +5 V, and two for +12 V. The manufacturer, however, decided to use only one of the +12 V channels available, resulting in this unit having a single +12 V rail.
This power supply uses a mix of solid and electrolytic capacitors in its secondary. The electrolytic capacitors are also Japanese, from Chemi-Con, and labeled at 105° C, as usual.