Why has my power supply died?

by Andy Turner
Coastal Computers & Design

Any PC repair business will tell you the same thing, they replace around 10 times as many power supplies than any other computer component. Why? Because many (if not most) power supplies fitted as standard equipment in the average mass-produced PC are poor quality.

You would think that manufacturers would specify better quality components in their systems. One reason they don’t may be that it’s easy to blame failures of this essential component on power surges and lightening strikes! If they can avoid doing unpaid warranty work then they will do so. Sure, these events can certainly account for a number of failures – and if you live in Shoalhaven Heads you will know and understand this, although I believe the mains supply situation has improved in the last few years.

As with most things, it all comes down to cost. A good quality modern power supply can cost anywhere from $70 to $150. With cheap computer cases (that usually always include a power supply) being available for under well under $100 it isn’t hard to see that the quality of some of the power supplies in them must be suspect. Price wars between computer makers means that every dollar that can be shaved off the component cost is another dollar that they can cut to compete against the opposition.

How can you tell if the power supply you have just had replaced was a cheapy? Not easily, but a good rule of thumb is to measure the weight of the part! There is a good correlation between the weight of a power supply and the quality and quantity of components inside!

The power rating of a supply doesn’t tell you much either – a quality 300 watt model from a good manufacturer will be far more reliable than a ‘500 watt’ cheapy. This is because the wattage rating depends on a lot of factors – including whether the supply is rated to supply this amount of power continuously or if it is only a peak power rating. Remember the old ‘music power’ ratings of stereos? Where a 500W PMPO (or peak music power) rated stereo actually could only manage around 40W of ‘real’ power output. Well, a computer supply usually needs to supply it’s output continuously and so the effect is that the supply ends up running very hot for most of it’s, often short, life.

Sure, a power spike or surge might ‘send it over the edge’, but the damage has already been done and this is the real reason that the part fails – it’s simply cooked itself by running outside it’s real rated limits. Another issue in Australia is that our mains supply is nominally 240V whereas most of the rest of the world it is 230V and the supplies available are usually 230V rated. Now, 10 volts might not sound much but when you add the maximum allowable mains fluctuations of plus or minus 6% then this is another stress that the supply has to cope with – and of course a poor quality one often won’t!

Usually, a failure of a supply doesn’t cause other problems, but I have had the odd PC that has come in with blown hard drives, modems and motherboards caused when a supply has blown, so I personally wouldn’t take the chance of fitting a poor quality part myself.

My advice for consumers then is this: if you are looking at buying a new computer, ask for a quality supply to be installed if there is any doubt in your mind that the standard one isn’t. Ratings are pretty meaningless really, but if it has a 500W supply and the case seems to be reasonably heavy then you should be fine. If you have a power supply failure on an out of warranty PC then ask for a better quality unit to be installed for you – $60 to $80 should get you a decent one.

Finally, computers that I sell (the Beecroft range) do have good supplies fitted. I have only replaced about 2 or 3 Beecroft supplies in total from memory while I would replace around 20 or so other makes every year.

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