Home / Tech News / Featured Tech Reviews / be quiet! System Power U9 700W PSU Review

be quiet! System Power U9 700W PSU Review

Efficiency

Our efficiency testing procedure is detailed here.

Using results from the previous page, we plotted a chart showing the SU9-700’’s efficiency at low loads, and loads from 10 to 110 percent of its maximum-rated capacity.


The efficiency under normal loads is high enough, always for the standards of this category, while with light loads it isn’t so competitive.

Efficiency At Low Loads

In the following tests, we measure the SU9-700’’s efficiency at loads significantly lower than 10 percent of its maximum capacity (the lowest load the 80 PLUS standard measures). The loads we dial are 20, 40, 60, and 80W. This is important for representing when a PC is idle, with power-saving features turned on.

Test # 12V 5V 3.3V 5VSB DC/AC (Watts) Efficiency Fan Speed (RPM) PSU Noise (dB[A]) PF/AC Volts
1 1.179A 0.498A 0.482A 0.197A 19.452 69.313% 622 9.8 0.871
12.175V 5.018V 3.313V 5.084V 28.064 115.34V
2 2.429A 0.997A 0.994A 0.394A 39.860 76.474% 618 9.7 0.926
12.172V 5.016V 3.312V 5.078V 52.122 115.31V
3 3.615A 1.495A 1.479A 5.072A 59.391 81.484% 618 9.7 0.962
12.170V 5.015V 3.311V 5.072V 72.887 115.28V
4 4.869A 1.994A 1.995A 0.790A 79.850 84.122% 638 10.2 0.962
12.168V 5.014V 3.310V 5.066V 94.922 115.25V

The fan’s speed is kept low under light loads while the efficiency levels are not that high. But this is an older generation design destined for users on a tight budget, so we shouldn’t expect for wonders here.

5VSB Efficiency

The ATX specification (revision 1.4), along with CEC, ErP Lot 3 2014 and ErP Lot 6 2010/2013, states that the 5VSB standby supply efficiency should be as high as possible, recommending 75 percent or higher with 550mA, 1A, and 1.5A of load.

The supply should also achieve higher than 75% efficiency at 5VSB under full load, or with 3A if its max current output on this rail is higher than 3A.

We take six measurements: one each at 100, 250, 550, 1000, and 1500mA, and one with the full load the 5VSB rail can handle.

Test # 5VSB DC/AC
(Watts)
Efficiency PF/AC Volts
1 0.100A 0.509 77.356% 0.051
5.088V 0.658 115.37V
2 0.250A 1.272 79.649% 0.117
5.085V 1.597 115.37V
3 0.550A 2.794 80.380% 0.221
5.080V 3.476 115.37V
4 1.000A 5.072 81.126% 0.315
5.072V 6.252 115.37V
5 1.500A 7.595 79.570% 0.377
5.063V 9.545 115.36V
6 3.000A 15.111 78.662% 0.453
5.037V 19.210 115.35V

The 5VSB rail registers high efficiency even under very light loads. It is nice to see a budget-oriented platform with a good standby circuit.

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 unit is in standby mode (without any load, at 5VSB).

Mode 12V 5V 3.3V 5VSB Watts PF/AC Volts
Idle 12.168V 5.022V 3.316V 5.088V 5.213 0.359
115.4V
Standby 0.044 0.003
115.4V

The vampire power is kept low with both voltage inputs. This is why the 5VSB rail achieves high efficiency under super light loads.

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 35°C (95°F) to 41°C (105.8°F) ambient temperature.

The next chart shows the cooling fan’s speed (again, in RPM) and output noise. We measure acoustics from one meter away, inside a hemi-anechoic chamber. Background noise inside the chamber is below 6 dB(A) during testing (it’s actually much lower, but our sound meter’s microphone hits its floor), and the results are obtained with the PSU operating at 35°C (95°F) to 41°C (105.8°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 is between 30°C (86°F) to 32°C (89.6°F).

For the majority of its operational range the unit’s output noise remains at very low levels, thanks to the highly relaxed fan profile.

Become a Patron!

Check Also

Cooler Master MM731 Wireless Review

It's ultra-lightweight as just 59g, plus it's wireless - but is it worth £90?