Why you can trust Tom's Hardware Our expert reviewers spend hours testing and comparing products and services so you can choose the best for you. Find out more about how we test.

Page 2 of 6:

Load Regulation, Hold-Up Time, Inrush Current, Efficiency and Noise

To learn more about our PSU tests and methodology, please check out How We Test Power Supply Units.

SilverStone ST1200-PTS

Corsair HX1200i

Seasonic SSR-1200GD

Primary Rails And 5VSB Load Regulation

The following charts show the main rails' voltage values recorded between a range of 40W up to the PSU's maximum specified load, along with the deviation (in percent). Tight regulation is an important consideration every time we review a power supply, because it facilitates constant voltage levels despite varying loads. Tight load regulation also, among other factors, improves the system’s stability, especially under overclocked conditions and, at the same time, it applies less stress to the DC-DC converters that many system components utilize.

Image 1 of 8

The load regulation is not tight, in all rails.

Hold-Up Time

Put simply, hold-up time is the amount of time that the system can continue to run without shutting down or rebooting during a power interruption.

Image 1 of 4

The hold-up time does not reach 17ms, as the ATX spec requires and to make matters even worse, the power ok signal is inaccurate. It is a huge disappointment, to see a high-end power supply reporting a "fake" power ok signal to the system's components, making them "believe" that they operate with safe voltages.

Inrush Current

Inrush current, or switch-on surge, refers to the maximum, instantaneous input current drawn by an electrical device when it is first turned on. A large enough inrush current can cause circuit breakers and fuses to trip. It can also damage switches, relays, and bridge rectifiers. As a result, the lower the inrush current of a PSU right as it is turned on, the better.

Image 1 of 2

The SilverStone ST1200-PTS registered inrush currents are among the lowest we have ever measured in a 1200W PSU, especially with 230V input.

10-110% Load Tests

These tests reveal the SilverStone ST1200-PTS’s load regulation and efficiency levels under high ambient temperatures. They also show how the fan speed profile behaves under under increased operating temperatures.

Swipe to scroll horizontally

Test #	12V	5V	3.3V	5VSB	DC/AC (Watts)	Efficiency	Fan Speed (RPM)	PSU Noise (dB[A])	Temps (In/Out)	PF/AC Volts
1	8.214A	1.990A	1.980A	0.986A	120.030	89.144%	940	21.5	39.48°C	0.978
11.984V	5.026V	3.329V	5.072V	134.648	42.26°C	115.10V
2	17.433A	2.991A	2.987A	1.186A	239.737	92.018%	943	21.5	40.96°C	0.993
11.979V	5.016V	3.316V	5.058V	260.534	44.56°C	115.10V
3	27.017A	3.496A	3.478A	1.388A	359.236	92.952%	946	21.6	41.05°C	0.996
11.964V	5.007V	3.306V	5.044V	386.474	45.65°C	115.10V
4	36.696A	4.002A	4.004A	1.591A	479.680	92.604%	951	21.7	41.91°C	0.997
11.949V	4.998V	3.296V	5.029V	517.989	47.82°C	115.10V
5	46.032A	5.014A	5.025A	1.795A	599.814	92.257%	956	22.0	42.03°C	0.998
11.933V	4.988V	3.284V	5.015V	650.155	48.57°C	115.10V
6	55.395A	6.029A	6.051A	2.001A	719.957	91.685%	1011	23.7	42.65°C	0.999
11.917V	4.978V	3.272V	4.999V	785.249	50.27°C	115.09V
7	64.747A	7.049A	7.089A	2.207A	839.669	91.037%	1644	35.4	43.51°C	0.999
11.901V	4.967V	3.259V	4.984V	922.342	52.05°C	115.09V
8	74.192A	8.076A	8.134A	2.416A	960.114	90.276%	2169	42.5	43.97°C	0.999
11.884V	4.955V	3.245V	4.969V	1063.527	53.23°C	115.08V
9	84.007A	8.596A	8.657A	2.420A	1079.426	89.554%	2189	42.6	44.42°C	0.999
11.867V	4.945V	3.235V	4.960V	1205.335	54.61°C	115.07V
10	93.675A	9.120A	9.213A	3.042A	1199.868	88.617%	2192	42.7	45.55°C	0.999
11.851V	4.936V	3.224V	4.933V	1353.995	56.74°C	115.06V
11	103.953A	9.133A	9.236A	3.048A	1319.885	87.644%	2196	42.7	46.95°C	0.999
11.834V	4.928V	3.215V	4.923V	1505.969	59.02°C	115.05V
CL1	0.142A	14.002A	13.996A	0.000A	117.534	86.273%	1022	24.2	42.17°C	0.981
11.985V	4.992V	3.282V	5.090V	136.235	48.47°C	115.11V
CL2	100.003A	1.001A	0.998A	1.000A	1198.758	88.973%	2202	42.7	45.64°C	0.999
11.855V	4.964V	3.258V	5.002V	1347.333	56.51°C	115.06V

The PSU doesn't have a problem operating at high ambient temperatures, despite the official 40°C rating. Even with 110% of its max-rated-output with 47°C ambient the unit performed well. Moreover, the PF readings are high in all tests, proving the effectiveness of the interleaved APFC converter.

We conducted the same tests with 100V input and we faced a problem in the tests #10 and #11. The PSU refused to operate properly with the 12V rail being close to 11V and after a couple of seconds it shut down. This means that the SilverStone ST1200-PTS cannot operate properly with 100V input, under full load at least, although SilverStone states that this unit supports an input voltage range of 100V to 264V.

20-80W Load Tests

In the following tests, we measure the ST1200-PTS's efficiency at loads significantly lower than 10 percent of its maximum capacity (the lowest load the 80 PLUS standard measures). This is important for representing when a PC is idle, with power-saving features turned on.

Swipe to scroll horizontally

Test #	12V	5V	3.3V	5VSB	DC/AC (Watts)	Efficiency	Fan Speed (RPM)	PSU Noise (dB[A])	PF/AC Volts
1	1.204A	0.496A	0.477A	0.196A	19.529	68.815%	928	21.3	0.702
11.993V	5.034V	3.340V	5.103V	28.379	115.12V
2	2.473A	0.993A	0.988A	0.393A	39.953	79.212%	935	21.4	0.891
11.992V	5.033V	3.337V	5.096V	50.438	115.11V
3	3.671A	1.490A	1.469A	0.590A	59.416	83.795%	936	21.4	0.930
11.991V	5.031V	3.334V	5.088V	70.906	115.11V
4	4.939A	1.988A	1.979A	0.787A	79.801	85.985%	938	21.5	0.959
11.989V	5.029V	3.331V	5.081V	92.808	115.10V

Under light loads the fan spins at low speeds, keeping the noise below 22 dB(A) so it is practically inaudible. The registered efficiency is satisfactory, given the PSU's 1200W capacity.

Efficiency

Next, we plotted a chart showing the SilverStone ST1200-PTS’s efficiency at low loads, and loads from 10 to 110 percent of its maximum-rated capacity. The higher a PSU’s efficiency the less energy goes wasted leading to a reduced carbon footprint, besides lower electricity bills.

Image 1 of 4

This is a highly-efficient design, going toe-to-toe with the Seasonic Prime Platinum with 1kW max power. With light loads, the ST1200-PTS performs well achieving the highest overall efficiency among 1200W units.

5VSB Efficiency

Swipe to scroll horizontally

Test #	5VSB	DC/AC (Watts)	Efficiency	PF/AC Volts
1	0.100A	0.511	72.896%	0.032
5.107V	0.701	115.09V
2	0.250A	1.276	78.378%	0.074
5.103V	1.628	115.09V
3	0.550A	2.802	79.989%	0.152
5.094V	3.503	115.10V
4	1.000A	5.082	80.821%	0.250
5.081V	6.288	115.09V
5	1.500A	7.601	80.298%	0.334
5.067V	9.466	115.10V
6	3.000A	15.072	78.174%	0.474
5.024V	19.280	115.10V

Satisfactory efficiency results from the 5VSB rail.

Image 1 of 2

Power Consumption In Idle And Standby

Swipe to scroll horizontally

Mode	12V	5V	3.3V	5VSB	Watts	PF/AC Volts
Idle	11.991V	5.032V	3.341V	5.109V	10.683	0.219
115.1V
Standby	0.074	0.003
115.1V

Image 1 of 2

Fan RPM, Delta Temperature, And Output Noise

All results are obtained between an ambient temperature of 37°C (98.6°F) to 47°C (113°F).

At up to 700W load the cooling fan spins at low RPMs. With higher loads, it quickly increases its speed and, with 960W load, it is close to 2200 RPM with the noise exceeding 42 dB(A).

The following results were obtained at 30°C (86°F) to 32°C (89.6°F) ambient temperature.

With up to 800W load the unit is silent. It takes more than 900W load to enter the 30-35 dB(A) range while, with more than 1000W, it passes the 40 dB(A) mark.

MORE: Best Power Supplies

MORE: How We Test Power Supplies

MORE: All Power Supply Content