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Seasonic SS-850KM Active PFC F3

We have already tested Gold-certified products from Seasonic: SS-560KM, SS-660KM and SS-760KM. The SS-850KM is in fact the last model in this series. Although Seasonic also offers 80 PLUS Gold compliant PSUs with wattage ratings of 1050 and 1250 watts, they belong to the XM rather than KM subseries and have larger dimensions.

Since we are already familiar with products based on the same hardware platform, we won't dwell upon the SS-850KM's interior design and accessories, which are in fact identical to those of its series mates, but will instead focus on our tests.



Exterior Design

The SS-850KM is no different from the other models in the series. It features all-modular design, a sophisticated case with lots of details and mounting elements, and matte black paint.

Like the rest of the same series, the single decorative element of the SS-850KM is the Seasonic logo on the back panel which can be seen even when the PSU is installed into a system case.

Circuit Design

As for the interior design, this 850-watt model differs from the other in the same series in such nuances like a larger number of capacitors.

We don’t see any other changes here. Like the other KM series models, the Seasonic SS-850KM has DC-DC converters for +3.3 and +5V voltages on the card with connectors for modular cables. There is a single large heatsink near the side panel and a few small fingered heatsinks on the output rectifiers.

The SS-850KM employs United Chemi-Con capacitors rated for an operating temperature of 105°C.

Cables and Connectors

The Seasonic SS-850KM comes with the following power cables:

  • One mainboard cable with a 20+4-pin connector (59 cm)
  • One CPU cable with a 4+4-pin connector (64 cm)
  • One CPU cable with an 8-pin connector (64 cm)
  • Two dual graphics card cables with two 6+2-pin connectors on each (59 cm)
  • Two cables with three PATA power connectors on each (55+15+15 cm)
  • One cable with two PATA power connectors (35+15 cm)
  • Two cables with three SATA power connectors on each (55+16+16 cm)
  • One cable with two SATA power connectors (35+15 cm)
  • Two adapters for two floppy-drive plugs each (15 cm)

The cables are identical to those of the 760W model from the same series. We can't find any fault with them.


When it comes to electrical specs, the SS-850KM differs from the other models in its series in the higher capacity of its +12V power rail which can deliver up to 840 out of its full 850 watts.

The combined load capacity of the +3.3 and +5V rails is lower compared to the other PSUs in this review. On the other hand, 125 watts is about twice as much as the majority of modern computers will ever need from these two power lines.

UPS Compatibility

Connected to our APC SmartUPS SC 620, the Seasonic SS-850KM was stable at loads up to 435 watts when powered by the mains. This seems to be the highest result we’ve ever observed in our PSU tests. They could switch to the UPS’s batteries at loads up to 320 watts, which is not a record, yet the best result in this review anyway.

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