Cooler Master GX 750 W Power Supply Review
Load Tests
Contents
We conducted several tests with this power supply, as described in the article Hardware Secrets Power Supply Test Methodology.
First we tested this power supply with five different load patterns, trying to pull around 20%, 40%, 60%, 80%, and 100% of its labeled maximum capacity (actual percentage used listed under “% Max Load”), watching how the reviewed unit behaved under each load. In the table below we list the load patterns we used and the results for each load.
If you add all the power listed for each test, you may find a different value than what is posted under “Total” below. Since each output can vary slightly (e.g., the +5 V output working at +5.10 V), the actual total amount of power being delivered is slightly different than the calculated value. On the “Total” row we are using the real amount of power being delivered, as measured by our load tester.
The +12VA and +12VB inputs listed below are the two +12 V independent inputs from our load tester. During this test both inputs were connected to the power supply single rail (+12VB input was connected to the power supply EPS12V connector and all other cables were connected to the load tester +12VA input).
| Input | Test 1 | Test 2 | Test 3 | Test 4 | Test 5 |
| +12VA | 5 A (60 W) | 11 A (132 W) | 16 A (192 W) | 22 A (264 W) | 27 A (324 W) |
| +12VB | 5 A (60 W) | 10 A (120 W) | 16 A (192 W) | 21 A (252 W) | 27 A (324 W) |
| +5V | 2 A (10 W) | 4 A (20 W) | 6 A (30 W) | 8 A (40 W) | 10 A (50 W) |
| +3.3 V | 2 A (6.6 W) | 4 A (13.2 W) | 6 A (30 W) | 8 A (26.4 W) | 10 A (33 W) |
| +5VSB | 1 A (5 W) | 1.5 A (7.5 W) | 2 A (10 W) | 2.5 A (12.5 W) | 3 A (15 W) |
| -12 V | 0.5 A (6 W) | 0.5 A (6 W) | 0.5 A (6 W) | 0.5 A (6 W) | 0.5 A (6 W) |
| Total | 148.8 W | 300.0 W | 448.9 W | 596.7 W | 742.8 W |
| % Max Load | 19.8% | 40.0% | 59.9% | 79.6% | 99.0% |
| Room Temp. | 45.3° C | 45.2° C | 46.4° C | 46.6° C | 48.4° C |
| PSU Temp. | 45.8° C | 46.2° C | 47.8° C | 51.2° C | 55.5° C |
| Voltage Regulation | Pass | Pass | Pass | Pass | Pass |
| Ripple and Noise | Pass | Pass | Pass | Fail on +3.3 V and +5VSB | Fail on +3.3 V and +5VSB |
| AC Power | 180.6 W | 356.6 W | 543.3 W | 745.0 W | 966.0 W |
| Efficiency | 82.4% | 84.1% | 82.6% | 80.1% | 76.9% |
| AC Voltage | 115.3 V | 113.7 V | 111.9 V | 109.2 V | 107.2 V |
| Power Factor | 0.978 | 0.988 | 0.993 | 0.995 | 0.997 |
| Final Result | Pass | Pass | Pass | Fail | Fail |
Cooler Master GX 750 W can really deliver its labeled wattage at high temperatures.
Efficiency is decent for a mainstream product if you pull up to 80% of the unit’s labeled capacity (i.e., up to 600 W), between 80% and 84%. At full load efficiency drops below the 80% mark, at 77%. This unit is 80 Plus certifie
d and as we have been exhaustively explaining in our reviews, Ecos Consulting, the company behind 80 Plus, tests power supplies at 25° C, while we test them between 45° C and 50° C, and efficiency drops with temperature. Therefore our tests are more rigorous (and more realistic) that those conducted in order to get the 80 Plus certification (click here to learn more). By the way, the 80 Plus website doesn’t list this power supply.
Voltage regulation was superb, especially for a mainstream product: all positive voltages were within 3% of their nominal values all the times. This is good because voltages are closer to their official values than allowed by ATX12V specification, which sets a 5% tolerance (10% for -12 V). The only exception was during test five, where +5VSB went a little bit out of this tighter range, but still within the allowed range.
The problem with Cooler Master GX 750 W was noise and ripple. During tests four and five noise level on +3.3 V and +5VSB outputs was higher than the maximum allowed (50 mV): 57.4 mV and 70 mV for +3.3 V during tests four and five, respectively, and 51.6 mV and 58.4 mV for +5VSB during tests four and five, respectively. Below you can see the screenshots from our oscilloscope during test five. The maximum allowed for +12 V is 120 mV. All these numbers are peak-to-peak figures.
Figure 14: +12VA input from load tester during test five at 742.8 W (66.6 mV).
Figure 15: +12VB input from load tester during test five at 742.8 W (72.4 mV).
Figure 16: +5V rail during test five at 742.8 W (37.4 mV).
Figure 17: +3.3 V rail during test five at 742.8 W (70.0 mV).
Let’s see if we could pull even more from Cooler Master GX 750 W.