300W to 450W: 20 Power Supplies on the Test Bench

Conclusions

We compared 20 power supplies in the 300W to 450W region today. The decision to write such a large roundup was made based on reader input, since that's what most users actually need for a modern PC. We hope that by including older models as well we have shown a good overview of the market. When people ask us what power supply they should buy in this low wattage segment, we were never really sure ourselves because there are so many different models and unfortunately most of them are complete crap. Users should realize when buying a 500W+ power supply that it simply cannot costs just $30 and still deliver decent quality.

Today, we saw some good models with excellent performance that only cost a few dollars more, and these are the ones worth purchasing. In the following paragraphs, our readers can choose the most important feature(s) and make their decision based on those aspects. In each paragraph, we will select the best option from the 20 power supplies we have tested today. Somewhat interesting to note is that there was only one fatality during testing: the Cooler Master eXtreme Power Plus didn't make it to 100% load and left this world with a loud bang.

Cable Length and Connectors

For some people cables and connectors are the most important factor in choosing a power supply. Let's start with the ATX connectors that include the 24-pin, 8-pin, and 4-pin connectors for the CPU. Most units today only provide the 24-pin and 4-pin connectors. Only two models come with an additional 8-pin connector -- or at least a second 4-pin connector that can combine to form an 8-pin connector. Corsair's VX450W has an additional 8-pin connector and so does the Seasonic OEM 400ET. Some of the units like the HEC model and the OEM unit from FSP have very short 30cm cables, which will be fine for a system builder or perhaps uATX cases but definitely creates issues in larger cases. HTPCs will be another region in which these power supplies would make sense. Cooler Master has mostly 35cm cables, which is also not very good but is still acceptable since the 4-pin connector is 50cm. The longest harnesses are the Corsair VX450W with up to 60cm. Most other units have an average length of 40cm to 50cm.

Anyone that wants to run a modern graphics card with these power supplies needs to check PEG availability first. Most units come with at least one 6-pin PEG connector, which will be sufficient for most midrange systems. The Enermax Liberty Eco, Silverpower, and Tagan SuperRock calm with two connectors each and are capable of running an SLI or CrossFire setup (or a single high-end card with two connectors). The length of these harnesses varies from 40cm to 60cm, which is fine for most systems where the power supply mounts at the top of the chassis.

When it comes down to peripherals, we always hear different opinions. Some users never use more than two connectors, one for the SATA hard drive and the other one for the optical drive. Some might even run a Raid setup and would need three connectors. Who actually needs all the connectors found on most power supplies? If there aren't at least four to six Molex and SATA connectors today, some immediately downgrade the unit, but does everyone need that many connectors? Well, if you run small home-servers or storage arrays for your complete movie or music collection it would makes sense, yes. Our units today come with similar numbers of connectors. Each one has around four to six SATA and Molex connectors, plus one or two Floppy connectors. The length differs tremendously since some units offer only up to 40cm length and Silverstone for example offers up to 90cm, which is excellent for larger cases. If you need a power supply with long cables and plenty of connection options, you should have a closer look at the Silverstone Element; it has the longest cable harnesses in our comparison.

DC Voltage Regulation and Quality

We all know voltage regulation is a vital factor for power supplies and the output quality is something not many companies can handle well. Today power supplies have it easier since motherboards provide their own voltage regulation onboard -- the small black-grayish boxes on the motherboard are the VRMs. With these VRMs, the motherboard controls all of the voltage going to the memory, chipset, and CPU socket. This development raises the question of why we don't have only a single output on power supplies. If you have a laptop then you will recognize that there is a simple power supply typically only provides one voltage, which is around 19V. There are other voltages needed by the system and that is done through these VRMs. We will have to wait and see if a single output specification will hit the industry; until then we are stuck with Intel's ATX standard and multi-output power supplies.

If you focus on stable DC voltages for your system we can recommend several power supplies. Voltage regulation is not a problem today since all the manufacturers from our roundup stayed well within specifications. The best regulation with only around 2-3% comes from Seasonic, and most companies buy from them. In this list, we have first the Seasonic S12II and the Corsair CX400W that do well with lower voltages. The Silverstone Element again comes up with very stable rails, and Cooler Master with the Real Power Pro looks impressive starting strangely with lower voltages and building slowly up to a higher level. PC Power & Cooling and Seasonic both have very stable 12V rails, which is even more important than the 3.3V and 5V rails.

The output quality is another important factor and here we see larger differences because high ripple is something every company needs to address. For example, the Cooler Master eXtreme Power Plus goes way out of spec with the 3.3V and 5V rail. The OCZ ModXStream Pro is also quite above spec with its lower voltage rails and the Seasonic OEM unit could not run within specs. On the 12V rails, the headroom is a little higher and all companies stay below 100mV where 120mV is allowed.

Efficiency

Today everyone is talking about being green and saving the planet with energy-efficient products. The efficiency is very important for most people since it not only shows that power supplies don't waste too much energy but also is a good indication of quality. To reach higher efficiencies the manufacturer needs to have a well designed PCB with good components. Higher efficiency is impossible to reach for example with an older design with passive PFC. We have seen lately very nice power supplies with up to 90% efficiency, and soon Seasonic will even have the first power supplies with 80 Plus Gold certification in the market. We have published several articles that explain about the pros and cons of this efficiency-hype at the moment and when it would be worth it to spend more money on a new higher efficiency power supply and when not.

It is very important that you know what kind of load your PC will work with most of the time when choosing a power supply. Most power supplies are most efficient with around half of their rated output (50% load). Checking our efficiency results we see that both units with passive PFC have very low efficiency, which means they are poor choices. If you need high efficiency, you are best off with the Silverstone Element that achieves up to 89% efficiency. Then the PC Power & Cooling Silencers are also very good with up to 86% efficiency and 85% in the lower regions of 20% load. The Enermax Pro82+ and Liberty Eco also operate efficiently and get our third and last recommendation.

Acoustic Noise

Acoustic noise is another field where we see strong opinions on both sides. Years ago that was not an issue at all because if you built a system yourself you didn't have a choice for silent components -- especially not the choice we have today. Most companies took a brute force approach to cooling, with powerful but noisy fans to counteract high heat levels. Today this situation has fortunately changed. There are numerous passively cooled products out there and companies like AMD and Intel try to develop energy efficient products as well as maximum performance options. The whole market has changed, which is why we have phrases like "silent computing".

Power supplies do get hot when operating at high loads; that is a fact. This heat needs to be exhausted from the housing and that requires a fan. When you have less heat you can lower the airflow inside of the power supply, which is why we have mostly low acoustic noise at lower loads. If you care about finding a quiet power supply, you should first start by choosing the right wattage to make sure it's not fully loaded during normal operation.

Our test results have shown that the Silverstone Element and the Tagan SuperRock are among the quietest power supplies in our roundup today. There are other models with low acoustics as well, for example the Seasonic S12II, the two new Cooler Master Real Power Pros, and the PC Power & Cooling's Silencers. All of these remain generally quiet even with higher loads; there's no aggressively audible noise creating pain for your ears.

Prices

As stated already, we were not able to get price quotes on all of the power supplies today. Some are not yet available, some are only offered in some parts of the world, and for others the representatives weren't able to get us a price in time. We will update prices as soon as they are available. For now we have US and Euro prices and the differences are rather big. The Silverstone Element was not available in the U.S. anymore, unfortunately, but Silverstone is getting together with Newegg to reintroduce the power supply.

Of course some of the units are very cheap, but looking at the performance we don't recommend and will never recommend flawed products. There are power supplies such as the Corsair CX400W that didn't stick out too much during testing but still offer a very attractive price tag. If you do have only around $50 to spend on a power supply we suggest you have a closer look at the Corsair CX400W, or the OCZ ModXStream Pro with 400W if you want cable management. OCZ must have something wrong with the prices right now, since this power supply costs much more in Europe than in the U.S. -- although that cheaper price of $55 might only be for Newegg since other shops show $75 and more.

If you want the best performance and the price is a secondary priority, we definitely recommend the Element series from Silverstone. This power supply managed to top both the noise and efficiency charts, and delivered good results across the board. If you aren't able to buy the 400W version in the country where you live, go for the 500W version instead. However, we do hope that Newegg and other e-tailers will begin selling the 400W model again.