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Asus ROG STRIX 750W Gold Power Supply Review

Correctly testing power supplies is a complex procedure and KitGuru have configured a test bench which can deliver up to a 2,000 watt DC load.

Due to public requests we have changed our temperature settings recently – previously we rated with ambient temperatures at 25C, we have increased ambient temperatures by 10c (to 35c) in our environment to greater reflect warmer internal chassis conditions.

We use combinations of the following hardware:
• SunMoon SM-268
• CSI3710A Programmable DC load (+3.3V and +5V outputs)
• CSI3711A Programmable DC load (+12V1, +12V2, +12V3, and +12V4)
• Extech Power Analyzer
• Extech MultiMaster MM570 digital multimeter
• Extech digital sound level meter
• Digital oscilloscope (20M S/s with 12 Bit ADC)
• Variable Autotransformer, 1.4 KVA

DC Output Load Regulation

Combined

DC Load

+3.3V
+5V
+12V
+5VSB
-12V
A
V
A
V
A
V
A
V
A V
75W
0.95
3.34
0.93
5.03
5.13
12.06
0.50
5.02
0.20
-12.05
150W
1.65
3.34
1.66
5.02
10.61
12.05
1.00
5.02
0.20
-12.04
375W
3.00
3.34
3.02
5.02
28.11
12.05
1.50
5.01
0.30
-12.04
565W
4.05
3.34
4.07
5.01
42.94
12.04
2.00
5.00
0.30
-12.04
750W
4.90
3.33
5.24
5.01
57.48
12.02
2.50
5.00
0.50
-12.04

Load regulation proves to be excellent, holding within 1.5%.

Asus ROG STRIX 750W Maximum Load
841W

We managed to reach around 841W before the unit would shut down gracefully, after the protection kicked in. This is around 91 watts more than the rated output.

Next we want to try Cross Loading. This basically means loads which are not balanced. If a PC for instance needs 500W on the +12V outputs but something like 30W via the combined 3.3V and +5V outputs then the voltage regulation can fluctuate badly.

Cross Load Testing +3.3V +5V +12V -12V +5VSB
A V A V A V A V A V
734W 1.0 3.34 1.0 5.02 60.0 12.01 0.2 -12.03 0.50 5.02
154W 15.0 3.33 15.0 4.97 2.0 12.06 0.2 -12.03 0.50 5.01

The unit passes our Cross Load testing without any problems. When hit with 60 AMPS the +12V rail held at 12.01 which is a reference result. It is unlikely in a real life situation you would be doing this, but its good to see the design is holding up extremely well under demanding situations.

We then used an oscilloscope to measure AC ripple and noise present on the DC outputs. We set the oscilloscope time base to check for AC ripple at both high and low ends of the spectrum.

ATX12V V2.2 specification for DC output ripple and noise is defined in the ATX 12V power supply design guide.

ATX12V Ver 2.2 Noise/Ripple Tolerance
Output
Ripple (mV p-p)
+3.3V
50
+5V
50
+12V1
120
+12V2
120
-12V
120
+5VSB
50

Obviously when measuring AC noise and ripple on the DC outputs the cleaner (less recorded) means we have a better end result. We measured this AC signal amplitude to see how closely the unit complied with the ATX standard.

AC Ripple (mV p-p)
DC Load +3.3V +5V +12V 5VSB
75W 5 5 10 5
150W 5 5 15 5
375W 5 5 20 5
565W 5 5 20 5
750W 10 5 25 5

Noise suppression results are superb, peaking at 10mV on the +3.3V and 5mV on the +5V rail under full load. The +12V rail peaks at 25mV under full load conditions. A fantastic showing all round.

Efficiency (%) 240V
75W
89.4
150W
91.3
375W
92.5
565W
91.8
750W
90.6

Efficiency is good for an 80 Plus Gold unit, peaking at around 92.5% at 50% load. At full load the power supply maintains an 90.6% efficiency level, which is impressive.

We take the issue of noise very seriously at KitGuru and this is why we have built a special home brew system as a reference point when we test noise levels of various components. Why do this? Well this means we can eliminate secondary noise pollution in the test room and concentrate on components we are testing. It also brings us slightly closer to industry standards, such as DIN 45635.

Today to test the power supply we have taken it into our acoustics room environment and have set our Digital Sound Level Noise Decibel Meter Style 2 one meter away from the unit. We have no other fans running so we can effectively measure just the noise from the unit itself.

As this can be a little confusing for people, here are various dBa ratings in with real world situations to help describe the various levels.

KitGuru noise guide
10dBA – Normal Breathing/Rustling Leaves
20-25dBA – Whisper
30dBA – High Quality Computer fan
40dBA – A Bubbling Brook, or a Refrigerator
50dBA – Normal Conversation
60dBA – Laughter
70dBA – Vacuum Cleaner or Hairdryer
80dBA – City Traffic or a Garbage Disposal
90dBA – Motorcycle or Lawnmower
100dBA – MP3 Player at maximum output
110dBA – Orchestra
120dBA – Front row rock concert/Jet Engine
130dBA – Threshold of Pain
140dBA – Military Jet takeoff/Gunshot (close range)
160dBA – Instant Perforation of eardrum

Noise (dBA)
75W
<28.0
150W
<28.0
375W
30.7
565W
31.8
750W 33.4

The fan in this unit is very quiet under most load conditions, and it is only in the last 10% of power delivery that the fan starts to spin up to compensate for rising heat. The ASUS beefed up heatsink design really works well, even for a modestly efficient (in 2019 anyway) ’80 Plus Gold’ rated unit.

Temperature (c)
Intake
Exhaust
75W
36
39
150W
38
44
375W
39
47
565W
45
55
750W
47
58

The large dual ball bearing fan works well to expel heat out the rear of the chassis. The overall results are very good indeed.

Maximum load
Efficiency
841W
90.3

At 841 watts, the efficiency level measures 90.3%. Not a practical situation to be running 24/7, but worth noting.

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