Which Power Supply Do I Use With an AMD Athlon System?

By: OnDaEdg 10/11/01

If any of you visit the overclocking forums with any kind of regularity like I do, you would notice that there is a ton of talk going on about power supplies. People asking others for advice on which power supply to buy, what brand name is better, how many watts should they get, etc etc. Why is there so much curiosity surrounding power supplies right now? The answer to that is simple:  modern  processors draw a whole lot of current and the power supplies we had been using just aren't powerful enough, especially for us overclockers. Here I will attempt to shed some light on this subject and hopefully provide some answers to all those questions everyone is asking. I will be using three power supplies (ATX). Two of them are rated at 300 watts and the other is rated at 420 watts. Let's get started.

First off, here are the test units:

1. SH 300 watt purchased at Computer Warehouse for $35.00 . They claim that this power supply easily powers all of their customers Athlon based computers.)
    
2. Sparkle FSB300-60BTV which can be purchased from an online site for $38.00 + 8.00 shipping. www.sparklepower.com
    
3. Enermax  EG451P-V 430 watt which can be purchased from an online site for $78.00 + 8.00 shipping. http://www.enermax.com.tw/

Test System: AMD Athlon 1.33 ghz at 1.85 volts
Abit KT7e motherboard
Hercules Geforce2MX video card
CPU stress test: Prime95 Torture Test

The SH Power 300W PSU Test:
The first PSU I tested was the SH unit I had picked up locally. It has a 300 watt rating. It's amperage ratings are as follows: +3.3v 14amps, +5v 30amps, +12v 12amps. The combined 3.3v and 5v power rating is 150 watts.

After installing the PSU and powered up the computer, I waited for the bios screen to appear, but it never did. As a matter of fact, all I got is the now famous Fans-Only syndrome that a lot of AMD users have experienced. It appears the system is on, yet the computer fails to produce any type of output to the monitor. Thinking that perhaps I had a bad PSU, I exchanged it for a new one only to get the very same result. This power supply obviously can not produce enough +5volt power to boot the system properly.

SH Power Supply with 1.33 ghz Athlon : FAILED

The Sparkle 300W PSU Test:
The second PSU I tested was the Sparkle 300 watt unit. It has a 300 watt rating as well. It's amperage ratings are as follows: +3.3v 28amps, +5v 30amps, +12v 15 amps.These amperage ratings are much higher overall than the SH unit, yet they both have a 300 watt rating. The combined +3.3v and +5v power rating is a minimum of 200 watts.

After installing the PSU, I powered up the computer. This time the computer booted right through the bios and into Windows without a hitch. Using VIA hardware monitor, I will monitor the +5v and +12 input at idle and while Prime95 Torture Test was running. At idle, the power supply showed +5.0v and +11.98v. Now let's see how it works under a heavy load. Under Prime95 Torture Test, the Sparkle PSU put out +4.85v and +12.07v.

The Enermax 430W Power PSU Test:
Now let's test the more expensive Enermax unit. It is rated at 430 watts. Its amperage ratings are as follows: +3.3v 35amps, +5v 44amps, +12v 15amps. The combined 3.3v and 5v power rating is 220 watts.

After installing the PSU, I powered up the computer. It booted through the bios and into Windows.  At idle, VIA Hardware Monitor showed +5.08  and +11.97 volts at idle. While Prime95 Torture Test was running, it showed anywhere from +4.88 to 4.91 volts and 12.10 volts.

At this point of the testing, the Enermax unit comes out slightly ahead. Does this finish the testing? Actually, there was one thing I would like to do. Having used many Sparkle PSUs in the past, I knew that SparklePower usually had incorporated pot-trimmers inside their supplies. These trimmers could be adjusted to increase or decrease the +5/+12v outputs of the supplies. I opened up the Sparkle unit and there were three dials that could be adjusted. The one that I am interested in is the white one. The orange ones are not of any use to us (Keep in mind that I am talking about Sparkle Power PSUs. Other power supplies may have different trimmers or none at all). This has to be done very carefully because these power supplies can be very dangerous when opened. Do not allow any bare metal such as a screwdriver to come in contact with anything other than the pot-trimmer! Using a screwdriver, I slowly adjusted the pot while the computer was on until VIA Hardware Monitor showed 5.08 volts at idle. It didn't visually look like I had turned the trimmer at all, but a slight bit of force exerted on the screwdriver and my idle voltage was exactly 5.08 volts.

My goal was to have the Sparkle unit achieve the same idle voltage as the Enermax. Once this was done, I ran Prime95 Torture Test. The results were pretty surprising.  It showed voltages of +4.91 and 12.17 respectively.  I was able to achieve slightly higher voltages using a power supply that cost roughly half of what the Enermax cost. Even though I had boosted the power output of the supply a tiny bit, the heatsink  (of the PSU) did not seem to get any warmer. It was still just barely warm to the touch.

Let's sum up what we have learned from this simple test:

• All power supplies with the same power ratings are not the same. This is obvious     since only one of two 300 watt power supplies could actually get the computer to boot properly.
   
• Total power ratings may actually be a very bad indicator of the quality of the supply. In my opinion,  we should look at the combined 3.3v/5v power ratings instead. These ratings are displayed on every ATX PSU. You can check for this by looking on the  amperage rating chart on the PSU. Somewhere on that chart it will tell the 3.3/5v combined power rating.
   
• Do not buy a power supply you have never heard of. Buy a high quality unit with a good reputation such as SparklePower, Enermax.,  and Antec.

One other thing to think about for you guys that run a lot of fans in your cases, make sure that the supply you purchase has a good +12v amperage rating as well. Both the SparklePower and Enermax units I tested were rated for 15amps at +12 volts. 15 amps is higher than most any other supply I have seen and they would both be good choices to power your fan-heavy systems.

Hope this simple test helps some of you choose the right power supply for your system.

Until next time, Ondaedg is out! ( for more OnDa PSU wisdom check out the "Linking PSU's" article)

If you have any comments or Questions please email me at OnDaEdg@ProCooling.com