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45 PSUs tested at very low loads: which one is the most efficient?

Power supplies tested when idle and under load from Intel Haswell CPUs

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Conclusion

We have to admit that it was a very good idea to test power supplies at much lower loads. Especially at 22.5 watts, some PSUs don't do very well in terms of efficiency. Values below 70% really aren't very good, and several even end up with less than 65%!

So do these new results call for new conclusions for our large round-up of 39 300-450 watt power supplies? Let's first look at the 300-380 watt segment. The Seasonic G-Series 360W earned the Hardware.Info Gold Award and at low loads it still has excellent efficiency scores: 74.6% at 22.5 watts and even 90% at 100W. The Silver Award went to the Seasonic S12II 380W, which unfortunately didn't do se well at lower loads. In a later review we wrote that, in the 300-350 watt segment, the Be quiet! Pure Power L8 300W currently is the best choice. With an efficiency of 74.8% at 22.5W and 88% at 100W this affordable power supply still score very well, and we can stick to our conclusion. The winnder of the Bronze Award, the Be quiet! System Power 7 350W, scores 72.9% at 22.5W which is better than average, plus it's a very affordable PSU. 

In the 400-450 watt segment, the Gold Award went to the Seasonic Platinum Fanless 400W. The 72.5% efficiency at 22.5W doesn't really fit that picture, however, even if it's still above-average. Four power supplies got the Silver Award: the Be quiet! Pure Power L8 430W CM, the Be quiet! Straight Power E9 450W, the PC Power & Cooling Silencer Mk III 400W and the Nexus Value 430W. The Pure Power L8 430CM doesn't score better than average at 22.5W, but the Straight Power E9 450W is the second-most efficient power supply here. The Silencer Mk III 400W does slightly better than average, along with the Nexus Value 430W. We can still recommend the Silver Awardee Be quiet! Pure Power L8 400W. An efficiency of 73.6% at 22.5W is very good.

The power supply with the best efficiency at low loads is clearly the Antec EarthWatts Platinum 450W. The downside of this PSU is that it's pretty noisy and kind of expensive. For this reason the Be quiet! Straight Power E9 450W is our first choice if you need a power supply that's very efficient at low loads. If you're building a PC without dedicated graphics card, the Be quiet! Pure Power L8 300W is the best buy in this category. We already liked that one, and even more so now.


Seasonic G-Series 360W
Be quiet! Straight Power E9 450W


Be quiet! Pure Power L8 300W


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