PSU Poser - more power for less money?

[dancingmatt]

Morning all

Got a power supply poser for you:

I was going to buy a 550W power supply for my PC. If I buy a 750W supply instead...

- will the 750W use less electricity than the 550W to run the same PC? (my logic is it will since it will be running at a lower % of its maximum transforming capacity)

- I guess it will also run quieter and cooler for the same reason?

You see, I'm thinking that if I buy the bigger PSU, not only will it give me spare power for if I add to my rig in future, but will actually be cheaper to run and save on energy in the meantime?

Am I right or wrong?

Ta

DM

[DanceswithUnix]

It just isn't that simple.

First, your fundamental premise "since it will be running at a lower % of its maximum transforming capacity" is backwards, as a switch mode PSU will struggle to run at low output.

Then there is the fact that most high output PSUs these days are 2 rail, so you are actually buying 2x275W in a single box if you buy a 550W PSU. I wonder if the 750W is just 3x250.

Some manufacturers quote an efficiency, but they aren't to any standard so you can't compare them between PSUs (and they will be on reasonable load as that makes them look better).

Cooler & quieter are down to how well it is designed, which is quite independant of power rating.

I like my Akasa PSU, which has a single 120mm fan that is quiet unless the machine goes under heavy load. Plenty of other PSUs have a similar design.

[vaio]

Look for a supply with high efficiency.......circa 80%.

Look at Seasonic/Tagan/Antec/Enermax.

[adlech]

Here's a great article about PSUs,
http://www.silentpcreview.com/article28-page1.html
More does not mean better....you have to take into account the manufacturer and efficiency of the unit. Look for something with an active power factor, AFC, for better efficiency but you can't go wrong with the companies named above.

[charleski]

The SilentPCReview article also makes the point that, even for well-built PSUs, you're better getting a unit that delivers just a bit more than your actual need, as it will then be operating in the region of peak efficiency. So basically, if you need 500W for your machine, you will be using less power with a 550W PSU than a 750W one, simply because the latter hasn't reached its peak efficiency at a load of 500W.