How to pick a good power supply for your PC – theory vs. practice

Welcome to the first of my guides on building a nice desktop PC set. It is developed on the basis of our Actina DIY series, encouraging users to manually build their systems and to learn more about the system components.

I am starting my presentations with the power supply, as there are lots of myths, old problems and issued around this area. The bullshit produced by whining users still persists in some forums or groups. Still, there are some claims about every power supply doing its best at half the rated load, which is completely absurd.

There is some truth to every myth!

Yes, that’s right! These truths are still valid today for old power supplies, or new low- and mid-priced products. As soon as you exceed the most common power option, up to PLN 250, you will get a design capable of delivering consistent performance across the whole rated power range. They experience problems with extremely low and high power use levels only.

Fortunately, power supply vendors are keen on offering new solutions; as a result, not only the 80 PLUS GOLD certificate is promoted, but also the PLATINUM standard. All identifications refer to the power ratings of the supply. The lower the power loss between the socket and the CPU, graphics card and other components, the better color code can be assigned to the product.

This certificate will not yield any particular benefits for you as consumers, such as a noticeable reduction of your electricity bill. Still, it proves that the main power supply components are well balanced, not prone to overheating. After all, any power escape in such an electronic system would involve a transition into heat.

As regards the 50% load myth, I verified it recently through independent testing of SilentiumPC Vero L2 500 W power supply. I found that the component was unable to generate a full rated power, because it simply shuts down before that. But as soon as we delivered 50% load, everything was working fine and stable, and the whole design was capable of maintaining proper voltage levels. There was even no significant ripple.

Why am I discussing this particular power supply? Because it is among the most popular products in Poland. Besides, new PCs priced at <PLN 4000 tend to consume about 300W, so they are very often driven by Vero L2.

No ripple is very important for the motherboard; with good power quality, capacitors need not be charged continuously. Hence, their power use is reduced and motherboard life is extended.

As soon as higher price thresholds are reached, you should spend about 7-10% of the price of the whole PC on power supply. A decent product class will give you years of peace, even if you overclock the machine. Also, you get long manufacturer warranties with such designs, up to 10 years.

A lot of new technology solutions appear, too – there are semi-passive or even fully passive power supplies. The fan will often start only when half the rated power is reached. So if you pick something that is certified for 750W, there is a chance you will never hear your power supply at work.

The advanced platform also features certain improvements in power transmission from the mains to the components.

As soon as you break the PLN 300 barrier, you can start choosing modular cables, Gold certificate, and the semi-passive mode I mentioned above. The highest priced power supplies feature a power consumption and voltage monitoring function, which is great for enthusiasts.

When is it all right to cut power supply costs?

Many PC building experts often say you should never try to seek savings on a power supply. Myself, I do not really concur. Naturally, I do not want to exaggerate and promote buying some PLN 15 scrap; yet for a low power consumption office PC, a 200W power supply such as those often delivered with the case is absolutely sufficient.

TFX is not a popular standard, yet there are new implementations launched all the time, with higher certificates, targeted at buyers with a preference for small and powerful PCs.

Which PC power supply should you choose?

The easiest way to choose a power supply is to use a load calculator. Just enter your PC specifications and the algorithm will compute the average power consumption. With this value, you can start looking for a product with appropriate power rating.

Stick to recognized manufacturers who offer long warranty periods, and look for performance certificates. These identifications tell you that a particular power supply conforms to general European standards, where adequate voltage levels are also specified.

It is also recommended to learn more about power supply manufacturers; there are many companies that will order products from the major players and add their logo only.

Incidents were reported when two technically identical power supply products available on the market are offered at dramatically divergent prices only on the basis of the housing color and logo. It may seem weird, but in fact every brand considers different factors in their pricing policies.

What is your pick – theory or practice?

Theoretically, you should buy a power supply with a huge reserve, so that they have to work at half their rated power, which is when you get optimum voltage levels.

In practice, however, the more advanced the power supply is, the smaller the gap.

In theory, you cannot try to cut your spending on a power supply.

In real life, you can do that in certain circumstances and experience no adverse effects. There are lots of office PC building brands on the market that have been offering cheaper and less powerful power supplies in their business lines for years.

After a few years, these PCs with their ‘poor’ power supplies get to off-lease centers where they are resold to consumers, sometimes with 24-month warranty periods. And you know what? They are hardly ever returned for repairs necessitated by a power supply.

In theory, the more rated power, the better.

In practice, the smarter the power supply design and the more advanced solutions used, the better. Sometimes, instead of a lavish 1000W with a low certificate, you should choose a solid 650W with 10-year warranty, and it will handle 500W consumption well.

As usual, the conclusion is that calculation and common sense prevail over eccentric fantasies and 1000W indication on the box. Today, it is no longer a war of rating plates, but rather of unique solutions and better noise reduction qualities.