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FSP Twins 500W Redundant PSU Review

The FSP Twins series combines the usability of a normal ATX PSU and the advanced features of a redundant server unit. The Twins 500W we're evaluating today addresses users that need an ultra-reliable PSU and are willing to pay for it.

Load Regulation, Hold-Up Time, And Inrush Current

To learn more about our PSU tests and methodology, please check out How We Test Power Supply Units. 

Primary Rails And 5VSB Load Regulation

Load Regulation testing is detailed here.

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Hold-Up Time

Our hold-up time tests are described in detail here.

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Our hold-up time result is very long since the bulk caps of both modules are utilized in this test. On top of that, we need to see a large number for a smooth transition to take place from one module to the other in case of a failure.

Inrush Current

For details on our inrush current testing, please click here.

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The inrush current is quite low with 115V input, while it's on the high side with 230V (still, we see less than 50A).

Load Regulation And Efficiency Measurements

The first set of tests reveals the stability of the voltage rails and the Twins 500W's efficiency. The applied load equals (approximately) 10 to 110 percent of the PSU's maximum load in increments of 10 percentage points.

We conducted two additional tests. During the first, we stressed the two minor rails (5V and 3.3V) with a high load, while the load at +12V was only 0.1A. This test reveals whether a PSU is Haswell-ready or not. In the second test, we determined the maximum load the +12V rail could handle with minimal load on the minor rails.

Test #12V5V3.3V5VSBDC/AC (Watts)EfficiencyFan SpeedFan NoiseTemps (In/Out)PF/AC Volts
12.337A1.995A1.988A0.990A49.7567.540%8233 RPM53.8 dB(A)37.05°C0.939
12.056V5.005V3.316V5.049V73.6640.97°C115.1V
25.726A3.001A2.990A1.190A99.7478.498%8782 RPM55.3 dB(A)38.99°C0.970
12.033V4.986V3.307V5.032V127.0643.43°C115.1V
39.471A3.515A3.514A1.395A149.8482.945%8844 RPM55.6 dB(A)39.16°C0.978
12.013V4.973V3.298V5.013V180.6543.82°C115.1V
413.224A4.034A4.009A1.600A199.7985.260%9124 RPM55.2 dB(A)39.44°C0.986
11.992V4.962V3.291V4.995V234.3344.60°C115.1V
516.646A5.052A5.029A1.805A249.7486.466%9294 RPM54.9 dB(A)39.89°C0.989
11.972V4.945V3.279V4.977V288.8345.52°C115.1V
620.082A6.090A6.055A2.015A299.7187.120%9609 RPM54.7 dB(A)40.52°C0.991
11.947V4.928V3.268V4.958V344.0246.43°C115.1V
723.524A7.126A7.084A2.225A349.7287.371%9836 RPM52.2 dB(A)41.14°C0.993
11.930V4.912V3.259V4.940V400.2747.53°C115.1V
826.992A8.180A8.127A2.436A399.7687.408%10316 RPM50.4 dB(A)41.98°C0.994
11.905V4.894V3.249V4.920V457.3548.73°C115.1V
930.915A8.711A8.673A2.440A449.7387.406%10718 RPM51.6 dB(A)42.88°C0.995
11.875V4.882V3.240V4.911V514.5350.12°C115.1V
1034.551A9.248A9.192A3.075A499.6787.196%11062 RPM52.5 dB(A)43.90°C0.996
11.865V4.869V3.231V4.877V573.0451.63°C115.1V
1138.834A9.258A9.211A3.078A549.6187.074%11556 RPM54.8 dB(A)44.62°C0.997
11.843V4.863V3.223V4.870V631.2052.90°C115.1V
CL10.099A16.026A16.004A0.004A131.3275.947%14706 RPM53.5 dB(A)43.43°C0.976
12.011V4.863V3.260V5.091V172.9147.57°C115.1V
CL241.624A1.004A1.003A1.002A507.2588.205%11013 RPM52.5 dB(A)44.03°C0.996
11.868V4.955V3.264V4.997V575.0851.42°C115.1V

Load regulation at +12V is satisfactory, but it's quite loose on the minor rails. Apparently, the frame's DC-DC converters need some modification in order to offer tighter voltage outputs.

Efficiency under light loads is pretty low because the output of two PSUs is combined, doubling their power losses. Moreover, under high ambient temperatures, both fans are quite loud. We also notice a fan bearing noise in the 8000-10,000 RPM range. For those of you who weren't expecting such high acoustic readings, remember that this is a server-class PSU running under tough conditions. In addition to costing more money, professional power supplies delivering increased reliability and redundant functionality also tend to be loud. If you don't want a noisy PC, stay away from this FSP offering.

FSP Guardian Screenshots

You will find several screenshots of the FSP Guardian software below.

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