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How to pick between two power supplies. Which will last longer and not kill other components?

Posted on 2005-03-14
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Last Modified: 2010-04-26
Hi, i sell a few computer system from my home and wanted some expert advise on power supplies.

I have had some problems with power supplies going dead.

I know that I'm using cheap power supplies and I should be using better ones

But to keep computer prices low.. especially computers priced at $275-399, I have no choice but to use power supplies that comes with the case (the case is only $25)

The power rating on it says 400W

Here is the question:

I have a choice between two cases /w power supply at the same price, the two power supplies in the cases are different brand but same max rating of 400W.

Which one should I use?  How do i test to see which one will last longer?

Is there a simple test with a multimeter or something to determine
a) which will last longer  
b) which one has higher power rating (actual)
c) which is safer for the components

Some power supplies die within 2-3 months and although i get free replacements from the distributor, it is a hassle to have to change them for the customers


Also, if i had a choice between two other power supplies, 450W and 550W and they are the same price, is there something i should look for to see which one is going to not die on me and be stable

thanks
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Question by:shpark82
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Assisted Solution

by:tmj883
tmj883 earned 800 total points
ID: 13534104
The simple test...the heavier power supply is the better one(same watt rating).
http://www.adecy.com/psu/
Nice tool...pay attention to the power distribution over the power rails.
T
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by:onedeej
ID: 13534995
what kind of components are you putting in the machine, I usualy dont have that issue when I build systems as I get a case/PSU bundle rated 2-3 times higher than the wattage I actually need, if you are running the processors, then you are likely going to need a very stable power supply as they usually come bundled with many other components on the motherboard, and when you go to the above site to figure your wattage, make sure you include ALL of the motherboards onboard features, as those will draw power wether you use them or not.
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by:Callandor
ID: 13535070
The weight test is a good comparison - good power supplies use large iron cores and heavy windings.  The other test is to look at the +12v rating - good power supplies deliver 18a or more on this rail.
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LVL 18
ID: 13535414
Look at your current ratings.  If you have a 12 volt that is 15 amps and one that is 22 amps, the 22 is going to be the better device as it can handle the higher currents.  Many of the newer, better ones are certified for P4 and AMD systems which require a greater current rating than the older motherboards.

You can also look for fans, besides weight.  Many higher end PS have a couple of fans to keep the components cooler.
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Expert Comment

by:Watzman
ID: 13538209

We can't answer the question based on the information provided, but other things being equal, tmj883 is right ... the simple weight of a power supply is an amazingly good indication of it's quality.  Not foolproof, but very good.  The stuff that makes a power supply good .... heatsinks, large wire sizes in transformers, more components, heavier cores, multiple fans, etc. .... all tends to add weight.

The ratings, unfortunately, are not of much use, they can't be relied on and don't tell you much about thermal characteristics or duty cycle or instanteous current capacity.

However, we all know that when you get both a case and power supply for $25 (or even anything up to about twice that), the power supply that you are getting is more or less junk.

[I'd take a 365 watt Enermax over a junk 500 watt supply any day, by the way]
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by:shpark82
ID: 13541051
Weight is something that is noticeable between Antec power supply and a generic 400W power supply.  It is very difficult to notice much difference in weight between two generic power supplies.  I'm just hoping there is a way to stress test a power supply in a simple matter and see how high it'll go before giving up and how stable the voltage remains with heavier load.

Also, if you have two generic power supplies of same price, one being 400W and other 500W, and 400W is heavier than the 500W, should i be using the heavier 400W power supply?
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Callandor earned 1000 total points
ID: 13541237
Take a look at the current output on each voltage, as well as the weight.  Again, I would use the one with more current on +12v simply because the demand is higher on that line on bootup, and that's where weaker supplies fail.
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by:Watzman
Watzman earned 200 total points
ID: 13541668
Truth is, you can't really do a good evaluation.  One of the very critical factors, for example, is transient response.  A CPU, for example, may draw 20 amps average, but may need instantaneous peaks of more than 80 amps.  However, these peaks are of very short duration -- microseconds.  Still, the various power supplies involved have to be able to meet those peaks, or the system may lockup or crash.  Same for the video card, especially a high-end ATI or NVidia card that requires a disk-drive 12 volt power lead.  The transient response requirement may be WAY above any "normal" spec of ANY power supply, but it's still a requirement that the supply be able to handle it if the system is to be stable.  There is no way for you to measure this with anything availalbe to you outside of an R&D lab.  So we come back to .... not specs, but weight.  The key to this, for example, is larger wire sizes and larger capacitors, but you'd have to take the thing apart and have a schematic to make any kind of meaningful evaluation.  However, larger wire sizes, larger transformer cores, larger capacitors, larger heatsinks ..... are all discernable in the increased weight of the power supply.  So that's what I come back to, even though I can't argue that it seems crude.

Regarding the heavier 400w supply vs. the lighter 500w supply, yes, I'd go there.  I use a lot of Enermax 365 watt supplies in high-end systems where others use 400, 450 and 500 watt supplies, and they work just fine.  The high-end Enermax supplies are "top drawer" in very way (although I hate their extremely long lead length, it makes a mess inside the cabinet).  I don't mean to imply that other supplies are not good, but at the same time, we all know .... you know .... that the cheap supplies that come with under $50 cases, well they are just not very good quality.
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Expert Comment

by:nobus
ID: 13542826
the only answer i can give you : sell them both for a period, after that evaluate the return of bad ones, and make your decision
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Author Comment

by:shpark82
ID: 13549551
few more questions

between two name brand power supplies of equal max power rating, such as antec, thermaltake, enermax, zalman, etc.

and if they are the same price with both 450W, which one should i choose?

also, with the new 24pin power supplies coming in, with much higher price tag, are they worth it? especially for the 24pin motherboards?

i mean...350W 24pin power supply cost just as much as a 450W 20pin power supply.  so..for a 24pin power supply, should i be using 350W 24pin ps or 450W 24pin ps?

is a 24pin ps more stable or give better power in any way? or are they just more efficient?

i have listed several questions, please answer all of them and the points have been raised to 500!
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Expert Comment

by:Watzman
ID: 13550057

I can't give you "brand" ratings, and I doubt if anyone else can.  As to the 24-pin power supplies, match the power supplies to the motherboards.  If the motherboard has a 24-pin power connectory, use a corresponding power supply.
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LVL 1

Author Comment

by:shpark82
ID: 13551736
i know that 24pin motherboards support 20pin power supplies either using the adapter or even just plugging them in, I'm wondering if there is any downside to this setup... please give detailed list of downsides to hooking up 20 pin ps to a motherboard with 24pin
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Expert Comment

by:Callandor
ID: 13551928
An overview of choosing a power supply: http://www.firingsquad.com/guides/power_supply/

If you were to choose between Enermax, Antec Truepower, PC Power & Cooling, Zalman, or Thermaltake Purepower, you would be ok with any one - they are all good brands with proven track records.  I got a Thermaltake PSU recently and it came with a 20-to-24 pin adapter, so the manufacturers think using an adapter is ok and sufficient.  24-pin power supplies just split up the power output differently - they are not inherently better.
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