Seasonic SS-300TFX 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 our review both were connected to the power supply single rail.
| Input | Test 1 | Test 2 | Test 3 | Test 4 | Test 5 |
| +12VA | 2 A (24 W) | 4 A (48 W) | 6 A (72 W) | 7.5 A (90 W) | 9.25 A (111 W) |
| +12VB | 1.5 A (18 W) | 3.75 W (45 W) | 5.5 A (66 W) | 7 A (84 W) | 9 A (108 W) |
| +5V | 1 A (5 W) | 2 A (10 W) | 4 A (20 W) | 6 A (30 W) | 8 A (40 W) |
| +3.3 V | 1 A (3.3 W) | 2 A (6.6 W) | 4 A (13.2 W) | 6 A (19.8 W) | 8 A (26.4 W) |
| +5VSB | 1 A (5 W) | 1 A (5 W) | 1 A (5 W) | 1.5 A (7.5 W) | 2 A (10 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 | 61.7 W | 121.6 W | 183.7 W | 236.7 W | 298.3 W |
| % Max Load | 20.6% | 40.5% | 61.2% | 78.9% | 99.4% |
| Room Temp. | 41.7° C | 40.7° C | 41.0° C | 41.8° C | 43.2° C |
| PSU Temp. | 34.6° C | 36.3° C | 38.3° C | 39.8° C | 41.1° C |
| Voltage Stability | Pass | Pass | Pass | Pass | Pass |
| Ripple and Noise | Pass | Pass | Pass | Pass | Pass |
| AC Power | 72.9 W | 140.4 W | 214.9 W | 279.2 W | 357.7 W |
| Efficiency | 84.6% | 86.6% | 85.5% | 84.8% | 83.4% |
| AC Voltage | 110.9 V | 110.4 V | 109.8 V | 107.7 V | 106.9 V |
| Power Factor | 0.993 | 0.992 | 0.995 | 0.996 | 0.995 |
| Final Result | Pass | Pass | Pass | Pass | Pass |
Seasonic SS-300TFX can really deliv
er its labeled power at high temperatures. We usually test power supplies between 45° C and 50° C, but since this is a low-wattage model it was difficult to keep temperature that high inside our thermal chamber, therefore we tested it between 41° C and 43° C – which are still pretty high numbers.
Efficiency was outstanding, being very high at all tests, including the 20% load (test one) and the 100% load (test five) tests.
Voltage regulation was superb, with all voltages inside 3% of their nominal values(i.e., voltages were closer to their nominal value than needed, as ATX spec allows voltages to be up to 5% from their nominal values, 10% for -12 V). This includes the -12 V output, which usually doesn’t like to stay within a tolerance this tight.
And finally we have noise and ripple, which were practically non-existent. In fact, this was the power supply with the lowest noise/ripple levels we’ve tested to date: at full load noise level at +12 V outputs was less than 10% of the maximum allowed! Below you can see the results for test number five. As we always point out, the limits are 120 mV for +12 V and -12 V outputs and 50 mV for +5 V, +3.3 V and +5VSB outputs, and all numbers are peak-to-peak figures.
Figure 15: +12VA input from load tester at 298.3 W (11.6 mV).
Figure 16: +12VB input from load tester at 298.3 W (11.4 mV).
Figure 17: +5V rail with power supply delivering 298.3 W (6.4 mV).
Figure 18: +3.3 V rail with power supply delivering 298.3 W (10.2 mV).
Now let’s see if we could pull more than 300 W from this unit.