Articles: Cases/PSU

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We first met Seasonic's Gold-certified X series PSUs back in 2010. A year later we tested their second generation which sported a substantially modified hardware platform. And now we’ve got Seasonic’s new X series PSUs with two platforms we have not tested previously. There are two models in the same wattage range as before (they are now referred to as KM3 instead of KM) and one model from the high-wattage XM subseries which goes from 1000 watts upwards.

The KM3 subseries is represented in our review with wattage ratings of 650 and 850 watts while the XM-indexed subseries is represented with the junior of the two currently available models which has a wattage rating of 1050 watts.

Testing Methodology

The following article offers a detailed description of our testing methodology and equipment and a brief explanation of what the specified and tested parameters of power supplies mean: X-bit Labs Presents: Power Supply Units Testing Methodology. If you feel overwhelmed with the numbers and terms this review abounds in, refer to the Methodology.

You can also go to our Cases/PSU section to check out reviews of all other PSU models we have tested in our labs.

We will mark the actual power consumption of three system configurations (discussed in our article PC Power Consumption: How Many Watts Do We Need?) in the cross-load diagrams. This will help you see if the tested PSU can meet the requirements of a real-life PC.

Testing Participants


Seasonic SS-650KM3 (X-650) and Seasonic SS-850KM3 (X-850)

We were somewhat confused when we first saw these products. We thought we had tested such PSUs already…

However, the model names were different from what we’d tested and the picture of the interior design was unlike anything we'd seen before.

The overall design of the packaging has not changed since the previous models of the series, though.

The packaging used to be individual for each model but is unified now for the entire series. The wattage and specs of the particular model are indicated on stickers.

The accessories haven’t changed, either. We can see a user manual, a set of single-use and reusable cable straps, mounting screws, a mains cord, and a Seasonic sticker for your computer case.

The PSU itself is traditionally packed into a velvety pouch.

The modular cables come in a dual-section bag made of some synthetic fabric.

Exterior Design

There are but few external differences we can note in comparison with the previous models.

The most notable one is the cooling system switch you can see next to the modular connectors. We've already seen it in Seasonic's Platinum-certified PSUs.

We can also see that the modular connectors take more space and the manufacturer had to remove any vents from that panel.

There are no differences from the previous models in this view.

Circuit Design

The SS-650KM3 (X-650) and SS-850KM3 (X-850), shown in the top and bottom photos respectively, are almost identical in their interior design excepting some differences in component ratings.

It is easy to see that the lower-wattage model has blue Hitachi AIC capacitors at the input whereas its higher-wattage cousin has brown United Chemi-Con capacitors there.

The overall circuit design has remained the same: active PFC and DC-DC converters located on the card with modular connectors. These PSUs are similar to their predecessors in smaller details, too.

The component layout is completely different, however. Even the card with DC-DC converters and modular connectors is not the same we saw in the previous models of the series, just because the configuration of connectors is different.

There is now a large aluminum heatsink instead of tiny individual ones on the field-effect transistors of the synchronous rectifier. The design and position of the daughter cards have changed as well. The input capacitors are closer to the corner of the case and one long heatsink is replaced with three small ones.

These PSUs employ an SRC/LLC+SR controller Champion Micro CM6901.

The standby source is based on an Infineon ICE2QR4765 chip.

There are electrolytic capacitors from United Chemi-Con at the output. They enjoy an excellent reputation.

All in all, the new features of Seasonic's latest X series PSUs are comparable to those we witnessed on the transition from their first to second generation: the internal layout is completely overhauled although there are no fundamental innovations. We’ll see shortly if these changes have affected the electrical parameters.

Cables and Connectors

The all-modular X-650 is equipped with the following connectors:

  • Connector for a mainboard power cable
  • Six connectors for CPU or PCIe power cables
  • Five connectors for peripheral power cables

Included with the X-650 are:

  • One mainboard power cable with a 20+4-pin connector (61 cm)
  • One CPU power cable with a 4+4-pin connector (65 cm)
  • One CPU power cable with an 8-pin connector (65 cm)
  • Two graphics card cables with two 6+2-pin connectors on each (56+10 cm)
  • One cable with three PATA power connectors (50+12+12 cm)
  • One cable with two PATA power connectors (30+12 cm)
  • Two cables with four SATA power connectors on each (40+12+12+12 cm)
  • One cable with two SATA power connectors (30+12 cm)
  • One adapter from a PATA power connector to a floppy-drive plug (10 cm)

The X-850 has the same cable system plus one more cable with two 6+2-pin connectors for graphics cards.

The selection of cables and connectors is quite sufficient and versatile. The single graphics card cables of the new PSUs are handier than the dual cables of their predecessors. The number of infrequently used PATA power connectors has been reduced from eight to five while the number of SATA power connectors has increased from eight to ten (but the connectors are placed with smaller spacing, which may be inconvenient in some cases).

Overall, the cable system has become more balanced and up-to-date compared to the PSUs' predecessors.


The SS-650KM3 (X-650) and SS-850KM3 (X-850) are similar to their predecessors in their specs and meet today’s requirements by being able to deliver most of their output power via the +12V rail. The load capacity of the less important +5V and +3.3V rails is rather low at 125 watts.

As their predecessors, these PSUs comply with the 80 PLUS Gold specifications. The warranty period has been extended from five to seven years, so the SS-650KM3 (X-650) and SS-850KM3 (X-850) match Seasonic’s Platinum-certified products in this respect.

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