Antec SmartPower 2.0 SP-450 ATX Power Supply

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For a fuller understanding of ATX power supplies, please read our article Power Supply Fundamentals & Recommended Units. Those who seek source materials can find Intel's various PSU design guides, closely followed by PSU manufacturers, at Form Factors.

For a complete rundown of testing equipment and procedures, please refer to the article SPCR's Revised PSU Testing System. It is a close simulation of a moderate airflow mid-tower PC optimized for low noise.

In the test rig, the ambient temperature of the PSU varies proportionately with its output load, which is exactly the way it is in a real PC environment. But there is the added benefit of a high power load tester which allows incremental load testing all the way to full power for any non-industrial PC power supply. Both fan noise and voltage are measured at various standard loads. It is, in general, a very demanding test, as the operating ambient temperature of the PSU often reaches >40°C at full power. This is impossible to achieve with an open test bench setup.

Great effort has been made to devise as realistic an operating environment for the PSU as possible, but the thermal and noise results obtained here still cannot be considered absolute. There are far too many variables in PCs and far too many possible combinations of components for any single test environment to provide infallible results. And there is always the bugaboo of sample variance. These results are akin to a resume, a few detailed photographs, and some short sound bites of someone you've never met. You'll probably get a reasonable overall representation of that person, but it is not quite the same as an extended meeting in person.

REAL SYSTEM POWER NEEDS: While our testing loads the PSU to full output (even >600W!) in order to verify the manufacturer's claims, real desktop PCs simply do not require anywhere near this level of power. The most pertinent range of DC output power is between about 65W and 250W, because it is the power range where most systems will be working most of the time. To illustrate this point, we recently conducted system tests to measure the maximum power draw that an actual system can draw under worst-case conditions. Our most powerful P4-3.2 Gaming rig drew ~180W DC from the power supply under full load ? well within the capabilities of any modern power supply. Please follow the link provided above to see the details. It is true that very elaborate systems with SLI could draw as much as another 150W, but the total still remains well under 400W in extrapolations of our real world measurements.

SPCR's high fidelity sound recording system was used to create MP3 sound files of this PSU. As with the setup for recording fans, the position of the mic was 3" from the exhaust vent at a 45° angle, outside the airflow turbulence area. The photo below shows the setup (a different PSU is being recorded). All other noise sources in the room were turned off while making the sound recordings.


It important to keep in mind that fan speed varies with temperature, not output load. A power supply generates more heat as output increases, but is not the only the only factor that affects fan speed. Ambient temperature and case airflow have almost as much effect. Our test rig represents a challenging thermal situation for a power supply: A large portion of the heat generated inside the case must be exhausted through the power supply, which causes a corresponding increase in fan speed.

When examining thermal data, the most important indicator of cooling efficiency is the difference between intake and exhaust. Because the heat generated in the PSU loader by the output of the PSU is always the same for a given power level, the intake temperature should be roughly the same between different tests. The only external variable is the ambient room temperature. The temperature of the exhaust air from the PSU is affected by several factors:

  • Intake temperature (determined by ambient temperature and power output level)
  • Efficiency of the PSU (how much heat it generates while producing the required output)
  • The effectiveness of the PSU's cooling system, which is comprised of:
    • Overall mechanical and airflow design
    • Size, shape and overall surface area of heatsinks
    • Fan(s) and fan speed control circuit

The thermal rise in the power supply is really the only indicator we have about all of the above. This is why the intake temperature is important: It represents the ambient temperature around the power supply itself. Subtracting the intake temperature from the exhaust temperature gives a reasonable gauge of the effectiveness of the power supply's cooling system. This is the only number that is comparable between different reviews, as it is unaffected by the ambient temperature.

On to the test results..

Ambient conditions during testing were 25°C and 20 dBA, with an input of 120 VAC / 60 Hz measured at the AC outlet. It was a couple of degrees warmer than usual in the lab, and the Intake Temp readings in the measured data table below reflects this.

DC Output (W)
AC Input (W)
Intake Temp (°C)
PSU Exhaust (°C)
Temp Rise (°C)
Fan Voltage (intake)**
SPL (dBA @ 1m)
Power Factor

NOTE: The ambient room temperature during testing varies a few degrees from review to review. Please take this into account when comparing PSU test data.
* See Section 3 on stability below
** See Section 6 for more information about the fan controller.


1. VOLTAGE REGULATION was within the 5% specified by ATX12V throughout the test, and the +3.3V and +5V lines were typically within 2-3%. The +12V line was consistently high throughout the test, but the total variance from high to low was small. The biggest voltage drop on the +12V line was seen at 400W and above, but it still stayed above 12V.

  • +12V: 12.24 to 12.54
  • +5V: 4.86 to 5.04
  • +3.3V: 3.27 to 3.32

2. EFFICIENCY was good for a model that does not claim to be top-of-the-line. While we've regularly seen efficiency curves that peak in the mid eighties, these are typically high-end models that cost significantly more. The best efficiency was not achieved in the SmartPower 2.0 until the 150W - 200W range, which some PCs may demand under heavy loads. However, most systems do not see sustained use at this level. Efficiency at the lower loads (<150W) where most systems operate was about average.


For the most part, the SmartPower 2.0 had no trouble powering the loads we placed on it. However, one of the protection circuits kicked in when we tried to go from 400W up to 444W. This happened repeatedly, every time we tried to reach full load. The power supply could be reset within ten seconds by cycling the AC power switch, which suggests that the problem was an overly sensitive protection circuit, not a failure.

The shutdown occurred with the +5V and +3.3V lines fully loaded and delivering their combined maximum of 150W. Small loads (<5W) were also placed on the -12V and +5VSB lines. A combined load of 21A (252W) on the two +12V rails could be handled without problems. However, adding a single ampere (12W) to the +12V line triggered an immediate shutdown. The same 12W increase could be achieved by adding power to the +5V or +3.3V line without causing the power supply to shut down, even though this exceeded the published specification for these lines.

It is possible (not likely, but possible) that the overcurrent protection was legitimately shutting down the power supply, if the specifications on the web site, not the box, are correct (see page 2 of this review). Adding 12W to the +12V line would have put the output power on the +3.3V, +5V, and +12V rails at 414W ? a pithy four watts over the "maximum" of 410W. However, as mentioned above, adding a similar load to either the +3.3V or +5V line did not have the same effect. The other factor to consider is that because the 12V line was actually at 12.25V at full load, the real load was about 6W higher than intended. But this seems a very small "overload" to cause instant shutdown.

We contacted Antec about this problem, and they sent us a second sample to see if it would behave the same way. Fortunately, it did not. The second sample reached the maximum of 444W load without any problem, and stayed running at that output level for some time.

Because the inability to reach full power was probably the result of an overly sensitive protection circuit, not a failure, the problem that we saw with the first sample is largely trivial. No ordinary system is likely to draw more than half of the load at which the first sample shut down. A dual processor, SLI system might peak around 400W, but such a system cannot be connected to this power supply without multiple adapters.

4. POWER FACTOR was typical for a unit without power factor correction, ranging from 0.60~0.66, increasing with power draw.


The flow-through design of the SmartPower 2.0 works very well. The temperature rise through the power supply stayed at just 5~6°C through almost all of its output range. At lower loads, this is fairly normal, but as the load increases, it is more impressive. Many power supplies we've tested had a thermal rise of well over 10°C at 400W load, whereas the SmartPower 2.0 managed to keep it to just 6°C.


The test environment is live, so readings are higher than would be obtained in an anechoic chamber readings, due to reflections and reinforcement of sound waves off the walls, ceiling and floor.

As with every power supply we test, the positive wire of each fan was tapped so we could measure the input voltage. The neutral line was tapped at one of the common ground wires via an IDE drive connector. However, this method initially gave us a reading of -12V ? obviously wrong. This implied that the fan control circuit is completely separate from the rest of the power supply.

So, we also tapped the common wire of each fan. No matter what load was placed on the PSU, both fans were always fed the same voltage, which should have meant that they were always at roughly the same speed. However this was not the case: The input voltage remained at 5.3V at low loads, but sometimes the exhaust fan was spinning, and sometimes it wasn't. Since the voltage did not change, there was no apparent reason for the rear fan to have suddenly started spinning.

For this reason, we were unable to determine experimentally how the rear (exhaust) fan is controlled. One possibility is that the fan itself is thermally controlled independently of the fan control circuit, but Antec could not verify this yet. So, the voltages reported in the data table above reflect the input voltage to the intake fan.

The fan control circuit seemed to have an odd side effect that dismayed many users in our forums: When the fan monitor cable is plugged into a motherboard, the rear fan runs at full speed ? making it useless for a quiet computer. However, unplugging the cable solves the problem and the fans behave as they should. Antec informed us that this problem had been noted and corrected after the first shipment that went out to retail.

Without the fan monitor cable plugged in, the rear fan does not spin at all when the temperature is low. This is excellent for silencers. It means that the only source of noise is the intake fan in the middle of the case, away from any direct paths to the user's ears. It also spins slowly enough that it is probably close to or below the ambient noise level in most rooms, effectively making it silent in a low power system. The low-profile intake fan is quite well-behaved, even at the relatively high starting voltage of 5.3V.

The exhaust fan begins to spin when the intake temperature reaches the mid-thirties ? at about 150W load in our test environment. The ambient temperature during this test was a bit higher than usual, which caused the fan to start earlier than it would have otherwise. The exhaust fan has a noticeable effect on the noise. It is louder, and there is a small amount of whine from the motor. Fortunately, the transition as the fan turns on is not very audible. There is enough hysteresis in whatever is controlling the exhaust fan that it ramps up slowly and smoothly. This was true of both fans: Changes in noise level were only audible when specifically listened for.

Once the exhaust fan turns on, the noise signature rapidly deteriorates. The intake fan also increases in speed with temperature, and by the time the intake temperature has climbed above 34~35°C, it is no longer acceptable for use in a quiet system. The twin 80mm fans sound worse than a single 120mm fan at the same measured noise level because there are two separate bands of motor noise, both of which are higher in pitch than a typical 120mm fan, making the noise harder to tune out.

MP3 Sound Recordings of Antec SmartPower 2.0 SP-450

Antec SmartPower 2.0 SP-450 @ <90W (21 dBA/1m)

Antec SmartPower 2.0 SP-450 @ 150W (27 dBA/1m)

Antec SmartPower 2.0 SP-450 @ 200W (32 dBA/1m)

There was no need to make recordings at higher power levels; it's simply too loud.

Sound Recordings of PSU Comparatives

Seasonic Tornado 400 @ 65W (19 dBA/1m)

Seasonic S12-430 @ 150W (19 dBA/1m)

Enermax Noisetaker 600W (2.0) @ 150W (27 dBA/1m)

Nexus 92mm case fan @ 5V (17 dBA/1m) Reference


These recordings were made with a high resolution studio quality digital recording system. The microphone was 3" from the edge of the fan frame at a 45° angle, facing the intake side of the fan to avoid direct wind noise. The ambient noise during all recordings was 18 dBA or lower.

To set the volume to a realistic level (similar to the original), try playing the Nexus 92 fan reference recording and setting the volume so that it is barely audible. Then don't reset the volume and play the other sound files. Of course, tone controls or other effects should all be turned off or set to neutral. For full details on how to calibrate your sound system to get the most valid listening comparison, please see the yellow text box entitled Listen to the Fans on page four of the article SPCR's Test / Sound Lab: A Short Tour.


The SmartPower 2.0 is a good choice for use in a quiet system as long as power requirements are not too heavy. Its noise floor is close to that of our low noise reference, the Seasonic S12, and it is considerably cheaper. That said, it cannot compare to the noise level of the S12 at high loads in a typical high-end system. Although they start out at the same noise level and even stay close to level, beyond around 150W output, the SmartPower gets noisier more quickly and at a lower temperature than the Seasonic. The low noise of the SmartPower 2.0 at low levels can be attributed to the intelligent flow-through airflow design that cools it very effectively.

Given the straight-through airflow design of this PSU, it is probably a good candidate for use in an Antec P180 case, where the thermal isolation of the PSU would ensure lower temperature at the intake, and thus keep the PSU running at idle-quiet levels even at high load. No other fan would be needed in the bottom chamber of the P180. However, extension cables would be needed for the 2x12V and main ATX connectors to use this PSU in a P180.

The inability of our first sample to deliver its full rated load is a fairly minor issue, related more to the artificial conditions of our test setup and luck of the draw than a serious design flaw. It would be more a cause for concern if the shutdown occurred at a lower load or if it was not related to a protection circuit. More serious is the short length of the cables, which restricts the cases in which the SmartPower 2.0 can be used and can make it difficult to route cables.

All in all, the SmartPower 2.0 is a solid choice for a low-noise system. Those who want a top-of-the-line "designer" power supply are advised to look elsewhere, but if functionality and price are your primary requirements, the SmartPower 2.0 should fulfill your needs.

* * *

Much thanks to Antec for the opportunity to examine this power supply.

POSTCRIPT: Efficiency Correction
October 22, 2005

Recently, we discovered that our power supply testing equipment and methodology were providing erroneously high efficiency results. In general, the biggest errors occurred at higher output load points above 300W. At lower output levels, the efficiency error was often no more than one or two percentage points. No other tested parameters were significantly affected.

Through a fairly arduous process of discovery, analysis and old fashioned problem solving, we modified our testing equipment and methodology to improve the accuracy of the efficiency results and described it all in the article SPCR's PSU Test Platform V.3. As part of this revision, we re-tested most of the power supplies on our Recommended PSU List. In most cases, the same sample was used in the second test.

The corrected and original efficiency results for all the re-tested PSUs are shown in in the article, Corrected Efficiency Results for Recommended Power Supplies. The relative efficiency of the tested power supplies has not changed. If the tested PSUs are ranked by efficiency, the rankings remain the same whether we use the original results or the new results.

This data is also being added to relevant reviews as postscripts like this one.

CORRECTED EFFICIENCY: Antec Smartpower 2.0 - 450
Target Output
Actual Output

In this case, our original efficiency calculations were either dead on or slightly too low except at maximum output, at which point it was a bit too high.

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