Seventeam ST-550P-AG 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 valu
e 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.
+12V1 and +12V2 are the two independent +12V inputs from our load tester and during our tests the +12V1 input was connected to the power supply +12V1 (main motherboard connector and peripheral power connectors) and +12V2 (video card power connector) rails at the same time, while the +12V2 input was connected to the power supply +12V2 rail (EPS12V connector).
The power supply label says that each +12V rail can deliver up to 18 A but combined they can deliver only up to 384 W. This is, in our opinion, a value that is too low for a 550 W product since nowadays most current/power is drawn from the +12 V outputs. So we used two different load patterns for our 100% load test. On the first one (test five) we respected the limits stated on the power supply label, where we were pulling far more power from +5 V and +3.3 V than a real PC would do. On the second pattern (test six) we increased current on +12 V and lowered on +5 V and +3.3 V. The results you can see below.
| Input | Test 1 | Test 2 | Test 3 | Test 4 | Test 5 | Test 6 |
| +12V1 | 4 A (48 W) | 8 A (96 W) | 12 A (144 W) | 15.5 A (186 W) | 16 A (192 W) | 18.5 A (222 W) |
| +12V2 | 4 A (48 W) | 8 A (96 W) | 12 A (144 W) | 15.5 A (186 W) | 16 A (192 W) | 18.5 A (222 W) |
| +5V | 1 A (5 W) | 2 A (10 W) | 4 A (20 W) | 6 A (30 W0 | 18 A (90 W) | 10 A (50 W) |
| +3.3 V | 1 A (3.3 W) | 2 A (6.6 W) | 4 A (13.2 W) | 6 A (19.8 W) | 17 A (56.1 W) | 10 A (33 W) |
| +5VSB | 1 A (5 W) | 1 A (5 W) | 1.5 A (7.5 W) | 2 A (10 W) | 2.5 A (12.5 W) | 2.5 A (12.5 W) |
| -12 V | 0.5 A (6 W) | 0.5 A (6 W) | 0.5 A (6 W) | 0.5 A (6 W) | 0.8 A (9.6 W) | 0.8 A (9.6 W) |
| Total | 114.4 W | 217.1 W | 329.8 W | 429.8 W | 554.1 W | 540.4 |
| % Max Load | 20.8% | 39.5% | 60.0% | 78.1% | 100.7% | 98.3% |
| Room Temp. | 46.8° C | 47.9° C | 48.6° C | 47.4° C | 49.6° C | 50.4° C |
| PSU Temp. | 49.7° C | 50.9° C | 52.1° C | 50.1° C | 50.1° C | 53.9° C |
| Voltage Stability | Pass | Pass | Pass | Pass | Pass | Pass |
| Ripple and Noise | Pass | Pass | Pass | Pass | Pass | Pass |
| AC Power | 142 W | 262 W | 402 W | 533 W | 723 W | 705 W |
| Efficiency | 80.6% | 82.9% | 82.0% | 80.6% | 76.6% | 76.7% |
| Final Result | Pass | Pass | Pass | Pass | Pass | Pass |
Seventeam ST-550P-AG presents efficiency above 80% if you pull up to 80% (440 W) from it. This is not the best result in the world but it isn’t the worst either. A power supply not being able to maintain efficiency above 80% at full load is very common. For its market segment (low-end) it has a very adequate efficiency.
Voltage stability was great, with all voltages inside spec all the times.
Ripple and noise were also at very good levels. Noise level at +12 V outputs was always below half of the maximum limit (except +12V2 at tests five and six, which was at 63.2 mV and 62 mV, respectively). Noise level at the +5 V was below half the maximum limit on all tests but test five, where it peaked 31 mV (still inside the 50 mV limit). Noise level at +3.3 V was the highlight of this product, below 10 mV (the limit is 50 mV) if you pull up to 80% (440 W) of the labeled maximum capacity.
We were only disappointed with ripple on -12 V output. Since this power supply uses a voltage regulator integrated circuit for this output we expected to see very little ripple, which wasn’t the case (between 70 mV and 76 mV depending on the load and still inside ATX specs). But this doesn’t change the good impression we had about this product.
Below you can see noise level when we were pulling 554 W (test number five) from this power supply. Just to remember, the maximum allowed for the +12 V outputs is 120 mV peak-to-peak and the maximum allowed for the +5 V and +3.3 V outputs is 50 mV peak-to-peak.
Figure 15: Noise level at +12V1 input from our load tester with the reviewed unit delivering 554 W (42.2 mV).
Figure 16: Noise level at +12V2 input from our load tester with the reviewed unit delivering 554 W (63.2 mV).
Figure 17: Noise level at +5 V input from our load tester with the reviewed unit delivering 554 W (31 mV).
Figure 18: Noise level at +3.3 V input from our load tester with the reviewed unit delivering 554 W (14.8 mV).
Now let’s see if we could pull even more power from Seventeam ST-550P-AG.