SilverStone SFX Series SX700-LPT PSU Review

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Efficiency, Temperature, And Noise


Our efficiency testing procedure is detailed here.

Using results from the previous page, we plotted a chart showing the SX700-LPT's efficiency at low loads and loads from 10 to 110 percent of its maximum-rated capacity.

SilverStone's SX700-LPT is the second-most efficient unit in this category behind the Lian Li PE-750. That model follows some Titantium-rated ATX PSUs pretty closely. The situation is exactly the same under light loads, where SilverStone's offering fares well.

Efficiency At Low Loads

In the following tests, we measure the efficiency of SilverStone's SX700-LPT at loads significantly lower than 10 percent of its maximum capacity (the lowest load the 80 PLUS standard measures). The loads we dialed were 20, 40, 60 and 80W. 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 SpeedFan NoisePF/AC Volts
11.191A0.492A0.475A0.194A19.6271.68%0 RPM0 dB(A)0.860
22.411A0.979A0.980A0.395A39.7082.59%0 RPM0 dB(A)0.944
33.633A1.471A1.485A5.049A59.7986.44%0 RPM0 dB(A)0.962
44.851A1.973A1.959A0.791A79.7788.74%0 RPM0 dB(A)0.980

Under light loads, the PSU operates passively so its noise output is zero. In addition, the registered efficiency levels are quite high; in three out of four tests the 80% mark is easily met.

5VSB Efficiency

The ATX specification states that 5VSB standby supply efficiency should be as high as possible, recommending 50 percent or higher efficiency with 100mA of load, 60 percent or higher with 250mA of load, and 70 percent or higher with 1A or more of load.

We take four measurements: one each at 100, 250 and 1000mA, and one with the full load the 5VSB rail can handle. 

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

The 5VSB rail is highly efficient.

Power Consumption In Idle And Standby

In the table below, you'll find the power consumption and voltage values of all rails (except -12V) when the PSU is idle (powered on, but without any load on its rails), and the power consumption when the PSU is in standby mode (without any load, at 5VSB).

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Mode12V5V3.3V5VSBWattsPF/AC Volts

Phantom power is low, according to our readings.

Fan RPM, Delta Temperature, And Output Noise

Our mixed noise testing is described in detail here.

The first chart below illustrates the cooling fan's speed (in RPM), and the delta between input and output temperature. The results were obtained at 43 °C (109.4 °F) to 46 °C (114.8 °F) ambient temperature.   

The next chart shows the cooling fan's speed (gain, in RPM) and output noise. We measured acoustics from one meter away, inside a small, custom-made anechoic chamber with internals completely covered in sound-proofing material (be quiet! Noise Absorber kit). Background noise inside the chamber was below 18 dB(A) during testing, and the results were obtained with the PSU operating at 43 °C (109.4 °F) to 46 °C (114.8 °F) ambient temperature. 

The following graph illustrates the fan's output noise over the PSU's operating range. The same conditions of the above graph apply to our measurements, though the ambient temperature was between at 28 °C (82.4 °F) to 30 °C (86 °F).  

The passive mode lasts up to 200W with no more than 5W load on the minor rails. As the load on the minor rails increases, it affects the unit's passive operation by significantly reducing its duration.

Still, the SX700-LPT is among the quietest SFX-L PSUs we've tested. Even under full load and with lower than 30°C ambient temperatures, the low-speed fan doesn't output more than 40 dB(A).

Contributing Editor

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

  • JQB45
  • powernod
    Purely disappointing!!.
    A permanent flaw (false power-good signal), combined with a periodical flaw (far out of specs ripple if this unit gets overloaded), are more than enough evidence in order for me to conclude that this PSU is a potential danger for the rest of the hardware!!.
    Once more, thanks for the great review Aris!
  • basroil
    I looked at the internals first, and from that assumed this thing would be an utter mess. Surprisingly it's only a mess... If it was rated as a 550W unit I would have just said the holdup time was disappointing, but as a 700W rated unit this thing goes in the junk list.

    And seriously, what were they thinking with that layout? One short and the thing will definitely fry and take down your circuit breaker with it. Considering the number of missed surface mount solder points, shorts are going to be likely.
  • gadgety
    Great review. Thank you.