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Seasonic X-Series 650W KM3 Power Supply Review

The Seasonic X-Series 650W KM3, like the 850W KM3 is right at the top of its respective class. No power supply is perfect, but the KM3 series exhibit no weaknesses and deliver stable, high quality power to the system.

Load regulation is class leading and there is no 650W supply we have tested as capable as the 650W KM3 in this regard. Our intensive cross loading test didn’t cause a problem for the unit with it delivering almost nominal results. Ripple suppression is excellent with the unit peaking well within specifications for +3.3V, +5.5V and +12V output.

The addition of a new fan S2FC/S3FC selector switch and flat ribbon style modular cabling just enhances the overall appeal to the extremely demanding enthusiast audience.

For those people looking to reduce system noise emissions then this deserves serious consideration. At a 500W power demand the fan was only spinning at a slow to moderate rate and was barely audible. Most gaming systems today will not even be demanding close to 500W power under load.

The X-Series 650W KM3 will also be a practical choice for a high end media center. The passive fan profile means the system will not add noise to the overall build, only really becoming audible at 550W or above.

You can pick up the Seasonic X-Series 650W KM3 power supply for £114.98 inc vat from Overclockers UK. It is a fairly expensive unit, but if you want the finest power for your system, then this is certainly worth the money.


  • Load regulation is excellent.
  • Ripple suppression is well within industry tolerance guidelines.
  • extremely passive fan configuration – very low noise.
  • 80 Plus Gold+ efficiency levels.
  • can deliver over 800W of power before shutting down.
  • Pure modular design.
  • 105c rated capacitors.
  • fan switch.


  • Expensive.

Kitguru says: Another quality, rock solid power supply from Seasonic.

Rating: 9.5.

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  • Black Mamba

    Excellent, as we would expect by now !

  • harris

    My only problem with Seasonic is the pricing, they may be great, but I can’t afford the products of theirs I want to buy, I have to get cheaper.

  • Alex

    I have their last 650W PSU and I am happy with it. I always thought ribbon cabling was worse than the fat sleeved cabling, but I was clearly wrong.

  • Stevie

    Great company, always buy their products, and they last many many years, never had a seasonic fail. wise to see corsair and other companies using their designs.

  • Ivan

    Just ordered one as I needed a new 650w, my thermaltake 750w died and it was noisy too.

    THanks for review

  • Darth Digglers

    Bah! Newegg dont list these as KM2 or KM3, what a mess. they needed to change the name to R2 or something so retailers would list them properly. they are all falling under the X series name, which is a mess.

  • djoCC22

    i 1 it!!! great product but not great price for me.. i need titanium cert…..