Rosewill CAPSTONE-550M 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 the behavior of the reviewed unit 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 powers listed for each test, you may find a different value than what is posted under “Total” below. Since each output can have a slight variation (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. In 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’s single +12 V rail. (The power supply’s EPS12V connector was installed on the +12VB input of the load tester.)
| Input | Test 1 | Test 2 | Test 3 | Test 4 | Test 5 |
| +12VA | 4 A (48 W) | 8 A (96 W) | 12 A (144 W) | 16.5 A (198 W) | 20 A (240 W) |
| +12VB | 4 A (48 W) | 8 A (96 W) | 12 A (144 W) | 16 A (192 W) | 20 A (240 W) |
| +5 V | 1 A (5 W) | 2 A (10 W) | 4 A (20 W) | 5 A (25 W) | 6 A (30 W) |
| +3.3 V | 1 A (3.3 W) | 2 A (6.6 W) | 4 A (13.2 W) | 5 A (16.5 W) | 6 A (19.8 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 | 116.5 W | 220.8 W | 334.5 W | 450.5 W | 548.8 W |
| % Max Load | 21.2% | 40.1% | 60.8% | 81.9% | 99.8% |
| Room Temp. | 45.3° C | 44.8° C | 45.2° C | 46.2° C | 47.6° C |
| PSU Temp. | 46.9° C | 46.0° C | 45.8° C | 46.8° C | 48.6° C |
| Voltage Regulation | Pass | Pass | Pass | Pass | Pass |
| Ripple and Noise | Pass | Pass | Pass | Pass | Pass |
| AC Power | 129.8 W | 243.3 W | 373.5 W | 513.2 W | 634.0 W |
| Efficiency | 89.8% | 90.8% | 89.6% | 87.8% | 86.6% |
| AC Voltage | 115.4 V | 114.6 V | 114.3 V | 111.6 V | 110.5 V |
| Power Factor | 0.981 | 0.990 | 0.993 | 0.994 | 0.995 |
| Final Result | Pass | Pass | Pass | Pass | Pass |
The Rosewill CAPSTONE-550M passed our tests with flying colors.
Efficiency was between 86.6% and 90.8%, virtually matching the 80 Plus Gold certification, which promises a minimum efficiency of 87% at light (i.e., 20%) and full loads, and 90% at typical (i.e., 50%) load. The small difference between what is promised (87%) and what we’ve seen (86.6%) during our full load test can be easily explained by AC voltage, which dropped from 115 V to 110 V, and also by the higher temperature under which we test power supplies.
Voltages were always closer to their nominal values than required (i.e., 3% regulation). The ATX12V specification states that positive voltages must be within 5% of their nominal values, and negative voltages must be within 10% of their nominal values.
Let’s discuss the ripple and noise levels on the next page.