Skip to main content

Seasonic Focus SGX 650W SFX-L PSU Review: Reliable Power, Tiny Form Factor

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 Percent – 200ms


Advanced Transient Response at 20 Percent – 20ms


Advanced Transient Response at 20 Percent – 1ms


Advanced Transient Response at 50 Percent – 200ms


Advanced Transient Response at 50 Percent – 20ms


Advanced Transient Response at 50 Percent – 1ms

Image 1 of 6

Image 2 of 6

Image 3 of 6

Image 4 of 6

Image 5 of 6

Image 6 of 6

The +12V rail has good transient response, for the standards of this category, and the 5VSB rail also performs well. The 5V rail's transient performance can be further improved while the 3.3V rail clearly needs more capacitance or an improved design, to restrict its deviations.

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.

Image 1 of 3

Image 2 of 3

Image 3 of 3

There is a tiny spike at 5VSB, which is barely noticeable. In the other two tests we notice a voltage step along with a small spike, after the rail settles down, which are nothing to worry about.

Ripple Measurements

Ripple represents the AC fluctuations (periodic) and noise (random) found in the PSU's DC rails. This phenomenon significantly decreases the capacitors' lifespan 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).

10% Load12.4 mV9.9 mV12.7 mV10.3 mVPass
20% Load13.6 mV11.4 mV13.1 mV10.6 mVPass
30% Load14.1 mV12.8 mV14.5 mV11.7 mVPass
40% Load15.2 mV13.9 mV15.1 mV12.2 mVPass
50% Load16.9 mV15.9 mV15.6 mV12.8 mVPass
60% Load18.5 mV17.1 mV16.9 mV14.1 mVPass
70% Load20.8 mV18.7 mV17.6 mV16.2 mVPass
80% Load21.8 mV20.6 mV18.8 mV18.3 mVPass
90% Load23.4 mV22.0 mV19.6 mV19.7 mVPass
100% Load24.8 mV23.3 mV21.4 mV18.9 mVPass
110% Load36.8 mV23.6 mV21.3 mV23.2 mVPass
Crossload 116.5 mV19.3 mV18.7 mV10.8 mVPass
Crossload 223.3 mV15.1 mV15.9 mV18.5 mVPass
Image 1 of 4

Image 2 of 4

Image 3 of 4

Image 4 of 4

The ripple suppression is good on all rails, without using cables with extra filtering (in-line) caps which most users hate since they are difficult to work with.

Ripple At Full Load

Image 1 of 4

Image 2 of 4

Image 3 of 4

Image 4 of 4

Ripple At 110-Percent Load

Image 1 of 4

Image 2 of 4

Image 3 of 4

Image 4 of 4

Ripple At Cross-Load 1

Image 1 of 4

Image 2 of 4

Image 3 of 4

Image 4 of 4

Ripple At Cross-Load 2

Image 1 of 4

Image 2 of 4

Image 3 of 4

Image 4 of 4

EMC Pre-Compliance Testing – Average & 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 stay below the corresponding limits.

MORE: Best Power Supplies

MORE: How We Test Power Supplies

MORE: All Power Supply Content

Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.