NZXT C Series 650W Power Supply Review

A quiet power supply with a fair price.

(Image: © NZXT)

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Primary Rails And 5VSB Load Regulation

The following charts show the main rails' voltage values recorded between a range of 40W up to the PSU's maximum specified load, along with the deviation (in percent). Tight regulation is an important consideration every time we review a power supply because it facilitates constant voltage levels despite varying loads. Tight load regulation also, among other factors, improves the system’s stability, especially under overclocked conditions and, at the same time, it applies less stress to the DC-DC converters that many system components utilize.

The load regulation is tight on all rails, with the only exception the 5VSB rail where load regulation is not so important, from the moment the rail is within the specified, by the ATX spec, voltage range. 

Hold-Up Time

Put simply, hold-up time is the amount of time that the system can continue to run without shutting down or rebooting during a power interruption.

The hold-up time is much longer than 17ms, which is what the ATX spec requires. Moreover, the power OK signal is accurate and exceeds 16 ms. 

Inrush Current

Inrush current, or switch-on surge, refers to the maximum, instantaneous input current drawn by an electrical device when it is first turned on. A large enough inrush current can cause circuit breakers and fuses to trip. It can also damage switches, relays and bridge rectifiers. As a result, the lower the inrush current of a PSU right as it is turned on, the better.

The inrush current is low with 115V and at normal levels with 230V input. 

10-110% Load Tests

These tests reveal the PSU's load regulation and efficiency levels under high ambient temperatures. They also show how the fan speed profile behaves under increased operating temperatures.

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Test #12V5V3.3V5VSBDC/AC (Watts)EfficiencyFan Speed (RPM)PSU Noise (dB[A])Temps (In/Out)PF/AC Volts
13.599A1.987A1.986A0.982A64.95184.810%0<6.0 45.12°C0.928
12.044V5.035V3.324V5.091V76.584 40.31°C115.13V
28.230A2.980A2.980A1.181A129.99988.830%0<6.0 46.26°C0.957
12.042V5.032V3.322V5.079V146.346 40.99°C115.13V
313.203A3.481A3.476A1.381A194.99989.930%0<6.0 47.72°C0.971
12.039V5.029V3.321V5.068V216.834 41.68°C115.13V
418.180A3.978A3.978A1.582A259.99990.076%0<6.0 48.57°C0.979
12.035V5.027V3.320V5.056V288.643 41.87°C115.12V
522.817A4.974A4.971A1.784A325.03189.870%56010.0 42.60°C0.984
12.032V5.027V3.318V5.044V361.668 50.04°C115.12V
627.392A5.972A5.969A1.987A389.30889.505%57210.5 42.91°C0.987
12.029V5.025V3.317V5.033V434.959 51.00°C115.13V
732.062A6.971A6.971A2.191A454.65988.798%81119.0 43.16°C0.988
12.025V5.022V3.315V5.019V512.016 52.27°C115.13V
836.731A7.971A7.966A2.396A519.95688.135%119731.4 43.75°C0.990
12.021V5.021V3.313V5.008V589.951 53.69°C115.13V
941.803A8.467A8.453A2.399A584.87887.493%154034.4 44.42°C0.991
12.018V5.020V3.311V5.001V668.484 55.08°C115.13V
1046.612A8.969A8.974A3.011A649.70486.704%207644.4 45.49°C0.991
12.014V5.018V3.310V4.981V749.333 56.53°C115.12V
1152.025A8.973A8.977A3.016A714.52785.940%212845.4 46.66°C0.992
12.010V5.016V3.308V4.974V831.422 58.32°C115.12V
CL10.099A12.000A11.999A0.000A101.35384.907%562 10.1 41.97°C0.951
12.040V5.027V3.320V5.093V119.370 50.54°C115.16V
CL253.997A1.000A1.002A1.000A662.03687.236%1940 43.2 45.90°C0.992
12.013V5.017V3.312V5.035V758.902 56.39°C115.13V

The PSU does not have any problem operating under high temperatures, and the fan profile only gets aggressive at full load. 

20-80W Load Tests

In the following tests, we measure the PSU's efficiency at loads significantly lower than 10% of its maximum capacity (the lowest load the 80 PLUS standard measures). This is important for representing when a PC is idle with power-saving features turned on.

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Test #12V5V3.3V5VSBDC/AC (Watts)EfficiencyFan Speed (RPM)PSU Noise (dB[A])PF/AC Volts

The efficiency levels are satisfactory, at light loads. 

2% or 10W Load Test

Intel plans on raising the ante at efficiency levels under ultra-light loads. So from July 2020, the ATX spec will require 70% and higher efficiency with 115V input. The applied load is only 10W for PSUs with 500W and lower capacities, while for stronger units we dial 2% of their max-rated-capacity.

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Test #12V5V3.3V5VSBDC/AC (Watts)EfficiencyFan Speed (RPM)PSU Noise (dB[A])PF/AC Volts

The PSU doesn't pass 70% efficiency with 2% load since the platform it uses is not compatible with the newest ATX spec (v. 2.52) 


Next, we plotted a chart showing the PSU’s efficiency at low loads, and loads from 10 to 110% of its maximum rated capacity. The higher a PSU’s efficiency, the less energy goes wasted, leading to a reduced carbon footprint and lower electricity bills.

With normal loads, the NZXT unit almost at the bottom of the chart, so things don't look so nice. The newer CWT platforms win the best places, while in the next positions, we find The EVGA G3 and Cooler Master V650 models. 

With light loads (20-80W) things, the C650 is close to the middle, with the four units above it registering notably higher efficiency levels, though.  Finally, this platform isn't tuned for increased efficiency at super light loads, so naturally, it cannot meet the competition with a 2% load. 

5VSB Efficiency

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Test #5VSBDC/AC (Watts)EfficiencyPF/AC Volts

The 5VSB rail needs an efficiency boost. 

Power Consumption In Idle And Standby

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Mode12V5V3.3V5VSBWattsPF/AC Volts
Standby    0.0450.007

The vampire power levels are low with both voltage inputs. 

Fan RPM, Delta Temperature, And Output Noise

All results are obtained between an ambient temperature of 37 to 47 degrees Celsius (98.6 to 116.6 degrees Fahrenheit).

(Image credit: Tom's Hardware)

(Image credit: Tom's Hardware)

The fan profile is not aggressive at all. Even in the worst-case scenario, the fan doesn't spin at its full speed. 

The following results were obtained at 30 to 32 degrees Celsius (86 to 89.6 degrees Fahrenheit) ambient temperature.       

(Image credit: Tom's Hardware)

(Image credit: Tom's Hardware)

The passive operation doesn't seem to be highly dependent on the load of the minor rails since the max combined power at 5V and 3.3V is low (still enough for today's needs). The fan spins at very low RPM up to 400W load, and it takes more than 525W to make it enter the 30-35 dBA zone, for a short period. In general, the fan profile is highly relaxed. 

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Contributing Editor

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