be quiet! System Power U9 500W PSU Review: Affordable and Quiet

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Transient Response Tests, Ripple Measurements and EMC Pre-Compliance Testing

Advanced Transient Response Tests

For details on our transient response testing, please click here.

In the real world, power supplies are always working with loads that change. It's of immense importance, then, for the PSU to keep its rails within the ATX specification's defined ranges. The smaller the deviations, the more stable your PC will be with less stress applied to its components. 

We should note that the ATX spec requires capacitive loading during the transient rests, but in our methodology we choose to apply the worst case scenario with no extra capacitance on the rails. 

Advanced Transient Response at 20% – 200ms

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Advanced Transient Response at 20% – 20ms

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Advanced Transient Response at 20% – 1ms

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Advanced Transient Response at 50% – 200ms

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Advanced Transient Response at 50% – 20ms

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Advanced Transient Response at 50% – 1ms

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The low capacity along with the outdated design don't allow for good performance in the transient response tests, which are of high importance since they simulate with great accuracy the conditions that a PSU will face in real life. The loads are never steady in a true system. On the contrary, they constantly change and there are times where the variations can be large, for instance during a game or when several HDDs wake up from a sleep mode.

The 3.3V rail clearly is the weak link in the chain here, since it fails in four tests, while, in all the rest its voltage level is low.

Turn-On Transient Tests

In the next set of tests, we measure the PSU's response in simpler transient load scenarios—during its power-on phase. Ideally, we don't want to see any voltage overshoots or spikes since those put a lot of stress on the DC-DC converters of installed components.

The 5VSB waveform is fine. In the second test we notice a small step and in the third test the voltage takes quite some time till it settles down to its nominal level.

Ripple Measurements

Ripple represents the AC fluctuations (periodic) and noise (random) found in the PSU's DC rails. This phenomenon significantly decreases the capacitors' life span because it causes them to run hotter. A 10°C increase can cut into a cap's useful life by 50 percent. Ripple also plays an important role in overall system stability, especially when overclocking is involved.

The ripple limits, according to the ATX specification, are 120mV (+12V) and 50mV (5V, 3.3V, and 5VSB).

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10% Load8.0 mV6.2 mV10.5 mV10.3 mVPass
20% Load10.7 mV6.1 mV11.1 mV9.0 mVPass
30% Load12.1 mV6.2 mV11.4 mV9.8 mVPass
40% Load14.3 mV7.1 mV12.0 mV10.9 mVPass
50% Load15.6 mV7.7 mV12.7 mV17.0 mVPass
60% Load17.1 mV7.8 mV13.6 mV13.2 mVPass
70% Load20.1 mV8.4 mV14.5 mV14.6 mVPass
80% Load23.4 mV9.0 mV17.3 mV17.1 mVPass
90% Load25.4 mV10.2 mV18.5 mV18.3 mVPass
100% Load45.5 mV22.4 mV21.6 mV20.2 mVPass
110% Load50.1 mV20.4 mV23.3 mV22.2 mVPass
Crossload 113.6 mV9.3 mV18.1 mV9.4 mVPass
Crossload 242.2 mV11.2 mV14.4 mV14.4 mVPass

The ripple suppression is impressive in every level up to the 90% load test. With full load, the +12V rail gets quite a beating since ripple almost doubles. However still it remains at low enough levels especially if you take into account this product's price. All in all, the performance is quite good in these tests.

Ripple At Full Load

Ripple At 110% Load

Ripple At Cross-Load 1

Ripple At Cross-Load 2

EMC Pre-Compliance Testing – Average and Peak EMI Detector Results

Electromagnetic Compatibility (EMC) is the ability of a device to operate properly in its environment without disrupting the proper operation of other close-by devices.

Electromagnetic Interference (EMI) stands for the electromagnetic energy a device emits, and it can cause problems in other close-by devices if too high. For example, it can be the cause of increased static noise in your headphones or/and speakers.

The conducted EMI emissions are kept low, with both average and peak EMI detectors. This means that the unit's EMI filtering stages do a splendid job.

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Aris Mpitziopoulos
Contributing Editor

Aris Mpitziopoulos is a contributing editor at Tom's Hardware, covering PSUs.