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Corsair RM Series 550W Power Supply Review

Manufacturer: Corsair

DC Load Regulation and AC Ripple

DC Output Load Regulation

To simulate real world and maximum loading conditions, the Corsair RM550 PSU was connected to the load testers and supplied with a constant 115 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 PSU while operating on 115 VAC, 60 Hz.

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As you can see, the RM Series 550W PSU produced very good load regulation on all of the outputs across a broad range of load. The all-important +12V output stayed within ±2%.   

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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 AC ripple and noise suppression results for the Corsair RM550 PSU were also good with the three primary rails staying below 50% of the max recommended guidelines.
 

September 23, 2013 | 02:15 AM - Posted by sergio (not verified)

What do you think, is it OK to use this power supply in bottom-mounted-PSU cases? My concern is fan outake in limited space and directed downwar.? On loads below 50%, what's going to be with heat dissipation?

September 23, 2013 | 08:18 AM - Posted by jonnyguru (not verified)

sergio: Fans in power supplies are intake, not exhaust.

September 23, 2013 | 04:22 PM - Posted by Anonymous (not verified)

2 pci-e connectors a positive? That should be a negative. All 550w psu's in this day and age should have 4 pci-e connectors.

September 24, 2013 | 05:45 AM - Posted by rrr (not verified)

Unless you plan on running stuff like 2x 670 or 2x 7950, which is pushing 550W unit, I disagree.

2 PCI-E is IMO fine for 550W. Not so for 650W OTOH.

December 16, 2013 | 05:43 PM - Posted by psumaster (not verified)

There are videocards coming with 3 PCI-E, so I think at least 3 would be a good number. 2 PCI-E should be the default for 400W units.

September 24, 2013 | 09:19 AM - Posted by Mark "Dusty" D (not verified)

Lee, on the Specifications and Packaging page, the efficiency and fan noise curves show the x axis as sytem load (watts), but it is expressed in percentages of full load. Conversely, on the DC Load Regulation and AC Ripple page, it shows the wattage being drawn but would be more helpful in percent of full load.

March 1, 2014 | 07:05 PM - Posted by Anonymous Cowerd (not verified)

Would like an article
that compares the cost between the common recommendation
by all to take a PSU that's double your consumption
and a PSU that's just enough above your system consumption.

Example for calculated comparison:
PC1 peek consumption is 380w - PSU is 450W.
PC2 peek consumption is 380W - PSU is 750W.
(both the same 80+ rate)

PC#1 would be far from optimal, but buying cost is low.
PC#2 is in middle of the bell curve efficiency chart,
but cost more!

since the drop between PSU #2 & #1 efficiency is just few percent's would it make buying the more expansive PSU worth while, for the average warranty of the PSU?

Such article would greatly benefit PCPER community.

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