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Cooler Master MasterWatt 550W Power Supply Review

Author: Lee Garbutt
Manufacturer: Cooler Master

DC Load Regulation and AC Ripple

Testing Methodology

Establishing an accurate load is critical to testing and evaluating a PC power supply.  PCPerspective’s power supply test bench can place a precise DC load on the PSU under test.  Each power supply is tested under controlled, demanding conditions up to its maximum rated load (at 40ºC). Our current suite of tests includes:

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•    DC Load Regulation
•    AC Ripple and Noise
•    Efficiency
•    Differential Temperature
•    Noise

The Cooler Master MasterWatt 550W power supply was evaluated on both features and performance.  A full range of equipment was used to test the power supply under controlled load conditions.  

•    (2) CSI3710A Programmable DC load (+3.3V and +5V outputs)
•    (4) CSI3711A Programmable DC load (+12V1, +12V2, +12V3, and +12V4)
•    (2) 200W Precision resistor load bank (+12V5 and +12V6)
•    Switchable precision resistor load bank (-12V and +5VSB)
•    Agilent 34401A digital multimeter (Accuracy ±0.0035% vDC)
•    Extech 380803 Power Analyzer (Accuracy ±0.5% of full scale)
•    DS1M12 "StingRay" digital oscilloscope (20M S/s with 12 Bit ADC)
•    Extech Model 407738 digital sound level meter (Accuracy ±1.5 dB)

The following connectors were used to attach the MasterWatt PSU to the PCPerspective power supply test equipment.

•    (1) 20+4 pin ATX
•    (1) 8-pin EPS/ATX12V
•    (2) 6-pin PCI-E
•    (6) SATA
•    (3) Molex

DC Output Load Regulation

To simulate demanding and maximum loading conditions, the MasterWatt 550W power supply was connected to the load testers and supplied with 120 VAC.  In this test we are interested in seeing how well a PSU can maintain the various output voltages while operating under different loads.  

The ATX12V V2.2 tolerance for voltages states how much each output (rail) is allowed to fluctuate and has tighter tolerances now for the +12V outputs.  I have also included a second table of expanded tolerances (±1% to ±6%) for reference.

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The following tables list the DC voltage results for the MasterWatt 550W Bronze PSU while operating on 120 VAC, 60 Hz.

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The voltage regulation was good, staying within ±3% of the recommended ATX guidelines for all of the outputs.

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AC Ripple and Noise on the DC Outputs

The amount of AC ripple and noise present on the DC outputs was checked using a digital oscilloscope.  This AC component may be present in the KHz range where most switching power supplies operate or it may be more prevalent at the 60 Hz line frequency.  We adjust the O-scope time base to look for AC ripple at both low and high frequencies.  The ATX12V V2.2 specification for DC output noise/ripple is defined in the ATX12V Power Supply Design Guide.

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Ideally we would like to see no AC ripple (repetitive) or noise (random) on the DC outputs – the cleaner the better!  But in reality there will always be some present.  I measured the amplitude of the AC signal (in millivolts, peak-to-peak) to see how well the power supply complied with the ATX standard.  The following table lists the ripple/noise results during all of the load tests for the main output voltages of interest.

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The MasterWatt 550W power supply also exhibited good AC ripple and noise suppression across the full range of loads.


December 3, 2017 | 10:17 PM - Posted by Pink Gnome (not verified)

Surprisingly good for the price. Is there really any practical difference in functionality of any system components between this powersupply and, say, seasonic platinum 550 watt?

December 4, 2017 | 12:22 PM - Posted by Lee Garbutt

Good question. The practical functionality is similar (they both convert AC mains power to the DC voltages required for a PC to operate) but how they do it, how well they do it, and potentially for how long they  keep doing may be quite different. The MasterWatt PSU is a mainstream PSU targeted towards the mass market/average user while the Seasonic Platinum PSU is targeted towards PC enthusiasts looking for a premium PSU.

Compared to the MasterWatt, a Seasonic Platinum PSU uses a more sophisticated design, more components, higher quality components, and includes a longer warranty. These differences result in higher efficiency, better voltage regulation, and reduced AC ripple and noise on the DC outputs, which can potentially make your system more stable and live longer.

December 4, 2017 | 09:11 PM - Posted by Pink Gnome (not verified)

Thanks for the detailed answer!

December 4, 2017 | 01:13 AM - Posted by Cyric (not verified)

I would like to know the OEM for this supply. Coolermaster has a history of using seasonic as an oem which is a good thing.

December 4, 2017 | 12:25 PM - Posted by Lee Garbutt

No, the MasterWatt 550W is not made by Seasonic. Cooler Master appears to be using HEC (based in Taiwan) as the OEM for the MasterWatt series.

December 21, 2017 | 01:43 AM - Posted by Tech We Love (not verified)

Could you test room temperatures at the different watt % usages ? I would like to know how much the room temp rises at each level of power usage.

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