The SilverStone SX700-LPT SFX 700W PSU Review

Hot Test Results

We do not usually have great expectations regarding the power output quality of SFX PSUs, as the few we have reviewed to this date displayed poor power quality figures. The SX700-LPT pleasantly surprised us by delivering both good voltage regulation and ripple suppression. Voltage regulation on the 3.3V/5V lines is at about 2.5% and the 12V line is even stronger, maintaining a regulation of 2% within the nominal load range. Filtering is good as well, with our instruments recording a maximum voltage ripple of 52 mV on the 12V line. The 3.3V and 5V lines both recorded a maximum ripple of 24 mV, for a design limit of 50 mV.

Although we performed our first cross-loading test without any issues, we could not complete the second cross-loading test that is meant to test the 3.3V and 5V rails - or any test with a load below 200 Watts for that matter. The reason is simple: the fan of the SX700-LPT is programmed to start only at loads above 150 Watts, regardless of the ambient temperature. We could not maintain operating temperatures with a load between 120 and 150 Watts inside our hotbox, the PSU was shutting down to protect itself. Therefore, we only performed tests with a load greater than 200 Watts.

We need to stress that this is a PSU rated at 40°C and we perform our testing at temperatures higher than 45°C - we could reduce the ambient temperature of our hotbox testing but we chose not to do so as the results would then not be comparable to those of our previous reviews.

The energy conversion efficiency of the SX700-LPT takes a significant drop inside our hotbox, especially under heavy loads, indicating that the internal temperatures of the PSU are uncomfortably high. The average efficiency reduction is 1.4%, with a high drop of 2.1% at 100% load. The active parts of the PSU are good and such an efficiency loss cannot be attributed solely to them, as they have to cope with very high internal temperatures that reduce the efficiency of even the best of parts.

As we started testing the PSU with a load of 210 Watts (30% of the unit’s capacity), the fan started right away. Noise levels were relatively comfortable until the load reached 400 Watts, at which point the fan started speeding up sharply, essentially reaching its maximum speed within a further load increase of only 120 Watts. The maximum noise output of the SX700-LPT is nearly 57 dB(A), which would be unbearable for the vast majority of consumers. Even with such a high noise output, the fan can barely keep the internal temperatures of the PSU at reasonable levels, clearly indicating that the SX700-LPT is not supposed to be operating under such harsh conditions.