NZXT C Series 650W Power Supply Review

A quiet power supply with a fair price.

(Image: © NZXT)

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Advanced Transient Response Tests

For details about 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 also choose to apply a worst case scenario with no additional capacitance on the rails. 

Advanced Transient Response at 20% – 20ms

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Advanced Transient Response at 20% – 10ms

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Advanced Transient Response at 20% – 1ms

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Advanced Transient Response at 50% – 20ms

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Advanced Transient Response at 50% – 10ms

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Advanced Transient Response at 50% – 1ms

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The transient response is satisfactory on all rails but the 3.3V one, where it should be closer to 3%. 

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 rail is almost flawless, while the 12V slopes have some small waves, which are nothing to worry about.

Power Supply Timing Tests

There are several signals generated by the power supply, which need to be within specified ranges. If they are not, there can be compatibility issues with other system parts, especially mainboards. From year 2020, the PSU's Power-on time (T1) has to be lower than 150ms and the PWR_OK delay (T3) from 100 to 150ms, to be compatible with the Alternative Sleep Mode.

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PSU Timings Table
T1 (Power-on time) & T3 (PWR_OK delay)

The PWR_OK delay is out of the 100-150ms region, so the PSU does not support the alternative sleep mode recommended by the ATX newest spec. The platform that the C650 uses, though, wasn't designed with the new ATX spec in mind. We expect Seasonic to release a new one to meet the new requirements. 

Ripple Measurements

Ripple represent 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-degree Celsius increase can cut into a cap's useful life by 50%. 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% Load14.1 mV10.3 mV10.2 mV6.7 mVPass
20% Load19.2 mV10.8 mV11.1 mV7.1 mVPass
30% Load21.8 mV11.3 mV11.1 mV7.8 mVPass
40% Load23.9 mV12.2 mV11.9 mV7.4 mVPass
50% Load21.7 mV12.5 mV12.8 mV7.9 mVPass
60% Load15.2 mV13.1 mV12.6 mV8.4 mVPass
70% Load14.2 mV13.2 mV12.9 mV8.5 mVPass
80% Load15.1 mV14.7 mV14.2 mV10.1 mVPass
90% Load15.9 mV15.6 mV14.3 mV10.8 mVPass
100% Load19.9 mV17.1 mV15.5 mV11.2 mVPass
110% Load22.6 mV17.0 mV15.7 mV11.6 mVPass
Crossload 120.5 mV17.3 mV15.1 mV7.3 mVPass
Crossload 219.7 mV13.6 mV12.2 mV10.1 mVPass

The ripple suppression is good, but given the inline caps we expected even better results here. Nonetheless, the C650 has the lowest ripple at 12V among than the other two Focus-based platforms (Asus Rog Strix 650 and Seasonic SSR-650FX). 

Ripple At Full Load

Ripple At 110% Load

Ripple At Cross-Load 1

Ripple At Cross-Load 2

EMC Pre-Compliance Testing – Average & Quasi-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 nearby devices.

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

(Image credit: Tom's Hardware)

Three spurs are exceeding the limits with the average EMI detector, but everything is good with the QP EMI detector, which is way more accurate. 

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Aris Mpitziopoulos
Contributing Editor

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