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**Praetor** · 03-28-2005, 05:48 PM

Section 02 - How do I go about picking a nice PSU?
What's Important? Whats more important than what?

Current distribution. Look at the power supplie's sticker, label or website. If it's the sticker you're looking at, you'll see something similar to this:
- What if there is no sticker? What if the website doesnt say? Then the power supply is, generally speaking, crap. Don't buy it.
- Ok I can see the ratings? How do I know if it's good? Looking at the ratings you'll see an entry for "+12v" or even multiple entries (i.e., 12V1, 12V2, 12V3 etc). Although there are some exceptions for the cases where there are multiple entries, just for a general feeling of the power supply, simply add up all the currents (measured in amperes, and usuall abbreviated with a A). In the example above, there are two 12V entries each with 18A so we have a sumtotal of 36A available to the 12V rail.
  
  As an absolute minimum, make sure the rating on the 12V rail is at least 18A. Dont' bother even considering te power supply if it's running less than this. Now note that this absolute minimum applies to people building extremely low-budget systems and for the rest of the buyers, strive to ensure that the rating is at least 22A (and given the pricing of 22A-28A PSUs there's not much reason to settle for an 18A one). Naturally, the higher this rating the better.
Voltage tolerance and hold-up time. Generally a bit more difficult to find out (especially the voltage tolerance), strive to get a power supply with a lower tolerance and a higher hold-up time. As noted before, the tolerance needs to be within a ±5% spread and the hold-up time should be at least 16ms.
Brand and reputation. Let's face it, not all power supplies makers produce high quality products and by the same token, not all the products made by a company are made equally. As such I am somewhat relucatant to have a listing of "good" brands. You can get a feel for some good brands by looking through the reccomendations
Wattage. So many people say "get a 500W PSU" or whatever but fail to realize that the wattage means nothing if all that power is being provided on the wrong rail. A case in point, consider the Thermaltake PurePower 480W - a decent wellknown brand, a seemingly decent wattage rating but looking a bit deeper we find some flaws:
- Uses the older 20pin main connector rather than the 24pin or 20+4 connector
- For all that wattage, this power suppy has a measily 18A on the 12V rail
  With the rest of the features being non-exceptional. So all in all? Not the greatst buy. But could we have done better? Absolutely. Looking at the cheaper Antec TruePower TPII-480 we have a cumulative 36A on the 12V line, better efficiency. better hold up and almost certainly better voltage regulation.

While not so much a point to look for but as an overal thing, make sure any power supply you buy uses either a 24pin (native) connector or a 20+4pin connector. This will ensure that your power supply will be somewhat useful as newer and newer computers come out. So, a summary:

What Makes a Good PSU?

Never ever, under any circumstances, seetle for less than 18A on the 12V line, strive to maintain a minimum of 22A on the 12V rail where possible, naturally the higher the better
Look for a power supply with a solid warranty: shoot for at least 3 years -- it's an indication of how much the manufacturer will stand behind their product
Stuff like PFC and Active PFC, while nice should be treated as bonuses: a power supply without such circuitry will still be able to provide clean, reliable power to your equipment
Make sure the holdtime is at least 16ms, some manufacturers sneak in seemingly good values everywhere else and skimp on the hold-time
Tight voltage regulation: if you're buying a decent power supply to start with you should be able to count on the bare minimum of ±5% tolerance however if you've come across a power supply with a tighter advertised rating, all the better! As for power supplies with adjustable pots, you can generally count on them having a voltage regulation of at least ±3%

Special Considerations

Unless you know what you're doing, try to avoid fanless/passive-cooled PSUs. The efficiency of a power supply as well as the stability of the rails is dependent on the operating temperature of the psu (i.e., the hotter it gets, the less power efficiency you'll have). Unless you absolutely need dead silence, go for a reduced-noise ouput PSU with a larger fan (the larger fan can provide the same amount of airflow for reduced rpms and thus reduced noise)
For those of you looking for power supplies with modular cables in order to tidy of the mess: modular power supplies are often not as good as the non-modular variety. The reasoning is that, by making things modular, you increase both the resistance at each of the joints (meaning a power loss) as well as the number of potential failure points in the power supply.

03-28-2005, 05:48 PM	#3 (permalink)
Praetor Administrator Join Date: Jul 2004 Location: Canada Age: 24 Posts: 19,943	Section 02 - How do I go about picking a nice PSU? *What's Important? Whats more important than what?* Current distribution. Look at the power supplie's sticker, label or website. If it's the sticker you're looking at, you'll see something similar to this: What if there is no sticker? What if the website doesnt say? Then the power supply is, generally speaking, crap. Don't buy it. Ok I can see the ratings? How do I know if it's good? Looking at the ratings you'll see an entry for "+12v" or even multiple entries (i.e., 12V1, 12V2, 12V3 etc). Although there are some exceptions for the cases where there are multiple entries, just for a general feeling of the power supply, simply add up all the currents (measured in amperes, and usuall abbreviated with a A). In the example above, there are two 12V entries each with 18A so we have a sumtotal of 36A available to the 12V rail. As an absolute minimum, make sure the rating on the 12V rail is at least 18A. Dont' bother even considering te power supply if it's running less than this. Now note that this absolute minimum applies to people building extremely low-budget systems and for the rest of the buyers, strive to ensure that the rating is at least 22A (and given the pricing of 22A-28A PSUs there's not much reason to settle for an 18A one). Naturally, the higher this rating the better. Voltage tolerance and hold-up time. Generally a bit more difficult to find out (especially the voltage tolerance), strive to get a power supply with a lower tolerance and a higher hold-up time. As noted before, the tolerance needs to be within a ±5% spread and the hold-up time should be at least 16ms. Brand and reputation. Let's face it, not all power supplies makers produce high quality products and by the same token, not all the products made by a company are made equally. As such I am somewhat relucatant to have a listing of "good" brands. You can get a feel for some good brands by looking through the reccomendations Wattage. So many people say "get a 500W PSU" or whatever but fail to realize that the wattage means nothing if all that power is being provided on the wrong rail. A case in point, consider the Thermaltake PurePower 480W - a decent wellknown brand, a seemingly decent wattage rating but looking a bit deeper we find some flaws: Uses the older 20pin main connector rather than the 24pin or 20+4 connector For all that wattage, this power suppy has a measily 18A on the 12V rail With the rest of the features being non-exceptional. So all in all? Not the greatst buy. But could we have done better? Absolutely. Looking at the cheaper Antec TruePower TPII-480 we have a cumulative 36A on the 12V line, better efficiency. better hold up and almost certainly better voltage regulation. While not so much a point to look for but as an overal thing, make sure any power supply you buy uses either a 24pin (native) connector or a 20+4pin connector. This will ensure that your power supply will be somewhat useful as newer and newer computers come out. So, a summary: *What Makes a Good PSU?* Never ever, under any circumstances, seetle for less than 18A on the 12V line, strive to maintain a minimum of 22A on the 12V rail where possible, naturally the higher the better Look for a power supply with a solid warranty: shoot for at least 3 years -- it's an indication of how much the manufacturer will stand behind their product Stuff like PFC and Active PFC, while nice should be treated as bonuses: a power supply without such circuitry will still be able to provide clean, reliable power to your equipment Make sure the holdtime is at least 16ms, some manufacturers sneak in seemingly good values everywhere else and skimp on the hold-time Tight voltage regulation: if you're buying a decent power supply to start with you should be able to count on the bare minimum of ±5% tolerance however if you've come across a power supply with a tighter advertised rating, all the better! As for power supplies with adjustable pots, you can generally count on them having a voltage regulation of at least ±3% *Special Considerations* Unless you know what you're doing, try to avoid fanless/passive-cooled PSUs. The efficiency of a power supply as well as the stability of the rails is dependent on the operating temperature of the psu (i.e., the hotter it gets, the less power efficiency you'll have). Unless you absolutely need dead silence, go for a reduced-noise ouput PSU with a larger fan (the larger fan can provide the same amount of airflow for reduced rpms and thus reduced noise) For those of you looking for power supplies with modular cables in order to tidy of the mess: modular power supplies are often not as good as the non-modular variety. The reasoning is that, by making things modular, you increase both the resistance at each of the joints (meaning a power loss) as well as the number of potential failure points in the power supply. __________________ ASUS P5K Premium WiFi-AP, Q6600@3.7 / ASUS P5ND, E6400@3.8 4GB OCz Platinum XTC 8500 / 4GB CorsairXMS2 6400 5x500GB Seagate 7200.10 / 2x500 Seagate 7200.10 OCz 8800GTX 768MB @ 630/800 / 2x Galaxy 8800GT SLI Last edited by Praetor; 07-14-2006 at 02:39 AM.