How does a power supply work? Why is it important to choose a sufficiently powerful and efficient model? We guide you through discussions of efficiency and tips for getting the best deal before we go on to explain why less can be more in the PSU market.
This piece is for the folks who'd like to learn more about the facts, technologies, and terminology behind PC power supplies.
Keeping The Explanation Simple
Don't worry; this won’t be complicated or boring. We’ll just quickly explain how a switching PSU works, then use examples to illustrate some of the most common technical issues. We’ll explain what efficiency, loss, and reactive power mean, and why those words are relevant to you. Then we’ll look at the possible and (more importantly) necessary protective measures before applying theoretical knowledge to practical examples.

Practical Examples
Big versus small, efficient versus high-performance; we're going to examine three different PCs based on a trio of different usage models, calculate the power supplies they really need, and then explain the right class of PSU to use in them based on quality and long-term environmental impact.
The Frequency Trick
Remember those ancient radios with the vacuum tubes? They were massively built and tended to be clunky, heavy, very functional-looking things. However, it wasn’t just the wooden frame contributing to their weight. The large, massive transformers added their part as well.
The point is, even back then, clever engineers were taking advantage of a neat trick of physics that would later come to be used in every modern switching power supply. In order to convert a high alternating current into a low one and achieve galvanic separation of currents, they used normal, albeit powerful, transformers with a core made of iron plates.
While a mains frequency of 60 Hz required a comparatively large transformer, the so-called output transformers that delivered much higher low-frequency signals between 100 Hz and 16 kHz could be built much smaller while handling the same power. By aggressively capping the frequencies at the lower end of the spectrum, it was possible to increase the power that could be handled by a transformer of the same size. With the invention and subsequent introduction of new components, such as powerful switching tubes, and later, semiconductors using the same underlying physical principle, this advantage was carried over into other fields, opening up new possibilities.
And How Does That Apply To My PC?
Due to the high overall power requirements of modern computers, a conventional transformer-based PSU is no longer capable of converting the mains power into the low voltages required by PC components. The transformer required for the job would be too large and consequently far too heavy. Instead, we use switching power supplies that employ the same frequency trick as the good old tube radio. Their job is to provide the required voltages and currents as efficiently as possible, while also reliably maintaining those levels. Analogue (linear) solutions are no longer viable solutions. Instead, we now rely on transistors as switches to convert the mains power into higher frequencies, allowing us to use smaller transformers to transmit high power levels. Indeed, this is where the term “switching power supply” comes from. We’ll cover how those work in more detail in the next chapter. Don’t worry, it’s all simpler than you might think.
- Brought To You By Granny’s Radio
- How A Switching Power Supply Works
- Efficiency, Efficiency, Efficiency!
- Of Power Factors, Apparent Power, And Effective Power
- How To Spot An Efficient PSU?
- Don't Get Burned: Safely Before Stinginess
- How To Determine Your Power Requirements
- The Power Window Is Important
- Example 1: The Office PC
- Example 2: Mid-Range Gaming PC
- Example 3: The Enthusiast’s System
- If You Don't Like Our Advice, Buy A Fire Extinguisher

The addition below would turn this from a great article into an incredible article
-------------BQ---------RA-----------SF-------------LC------------HM-----------Hrs
Idle----------53.2---------56.7---------60.8---------68.2---------72.1---------4
Normal-----91.6---------90.4---------92.2---------98.9---------102.5-------4
Load--------125.6-------124.8-------122.2-------131.7-------136.4-------1
Off------------5.32---------5.67---------6.08---------6.82---------7.21---------15
Watt-hrs-per-day
----------------213----------227----------243----------273----------288
----------------366----------362----------369----------396----------410
----------------126----------125----------122----------132----------136
----------------80------------85------------91------------102----------108
Units-per-day
----------------0.78---------0.80---------0.83---------0.90---------0.94
Units-per-year
----------------286----------291----------301----------329--------344
Cost-@-15p/unit
--------------£42.96-----£43.70-----£45.19-----£49.41-----£51.63
Apologies for the formatting - WSIWIG please please pleaseits 2011 for crying out loud, just spent 5mins putting spaces instead of tabs and its still looses formatting
Wonder how long that 450w superflower could have kept running on full load.
But glad I've always stuck with Corsair & Enermax.
I only use the cheaper cooler master ones(something like this http://tinyurl.com/3wxcs3t) for my file server. No high drain, just a few HDDs.
A long time, although its overall lifetime would likely have been shortened running it at 110% load for extended periods. Their last two generations have been fantastic, just wish you could actually get them that cheap in Europe!
And saying all current-gen quads use the same amount of power is just silly Toms! The top-end Phenoms can creep past 130W at full speed, but the i5-2500k uses barely half as much, not 125W!
i had a 600watt winpower supply
it ran fine for 4 years
then there was an electronic whine coming from it under load it frove me crazy
it was a 5 or 600 watt i beleive i know a core 2 duo and hd 4670 cant draw that much power
could get a decent brand one at a local shop so had to go for a gigabyte 550 (450 watt continuos power supply)
im not kidding ive had quiter hair dryers!!!!