Gaming motherboards

Intel_man

Intel_man

VIP Member
EINREB said:
What makes a psu cheap? 550W is 550W. They might divide the Wattage in different output Voltages and ratings that you want, but that does not make it necessarily cheap.
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Judging a PSU purely on it's wattage output is not a good idea. Honestly, the most important figure on a PSU is the amount of amps on the +12V rail and if the PSU has a single +12V rail with lots of amps or 2 +12V rails with lower amp capacity per rail.

The 80 plus rating is also a good reference for quality.
 
Geoff

Geoff

VIP Member
EINREB said:
What makes a psu cheap? 550W is 550W. They might divide the Wattage in different output Voltages and ratings that you want, but that does not make it necessarily cheap.
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beers said:
That's entirely the issue. Plenty of low end companies like Diablotek will slap a 500w sticker on a 350w unit. Plus a lot of low end units will just inflate numbers on the label that aren't accurate to capacity.

350w of a 550w PSU on the 5v rail gives you effectively nothing. Most quality units will be rated near the max capacity of the unit on the 12v rail alone.

"550w is 550w" is also a flawed argument as there are other aspects of power delivery such as ripple and cross-load voltage stability that can vary greatly between units. A lot of low end ones don't even meet the ATX spec and can deteriorate the life of your components or introduce stability issues.

This might help give you some more info:
http://www.johnnylucky.org/power-supplies/psu-lemon-list.html
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let's also not forget the price of the components used to make the power supply. As they say, you get what you pay for. There's a reason lots of Chinese products are extremely cheap for what looks to be a comparable product, but end up failing rather soon. Tons of stories out there of cheap power supplies melting or catching fire due to poor quality components and construction. Even if nothing catastrophic happens, with low quality components you are looking at max power (i.e. the rated power), being sustainable for a much shorter amount of time. Plus you then have to worry more about voltage drops.
 
johnb35

johnb35

Administrator
Staff member
EINREB said:
What makes a psu cheap? 550W is 550W. They might divide the Wattage in different output Voltages and ratings that you want, but that does not make it necessarily cheap.
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Would you buy this piece of crap for $19?

http://www.newegg.com/Product/Product.aspx?Item=N82E16817170010&ignorebbr=1

It has 38 amps on the 5 volt rail compared to only 25 amps on the 12 volt rail and having a total of only 400 watts.

or this better psu for $30

http://www.newegg.com/Product/Product.aspx?Item=N82E16817438015&ignorebbr=1

with 34 amps on the 12 volt rail and with a total of 408 watts. Pretty good specs on that one.

A decent 500 watt psu will have around 40 amps on the 12 volt rail and at least 85-90% of its total wattage on the 12volt rail.
 
T

TrainTrackHack

VIP Member
There are other issues with cheaper units too, you'll probably find that 550W for a low-quality unit means at most 550W for very short periods of time under ideal ambient temperatures across all rails, none of which helps if the given amount of power needs to be supplied continuously on the 12V rail, especially if it's a warm day. Better power supplies have more protections in place too; overloaded, a good unit will simply turn off, whereas a cheap unit literally catching fire is not unheard of.

Relevant:
 
E

EINREB

Member
Makes sense. I was looking at it from an engineering standpoint, not from a reliability one. To me, once you have established your requirements as far as power consumption is concerned, you have established your needed wattage. The trick is to determine how well the psu maintains the required power load, and you should be able to find that in the specs.
 
Intel_man

Intel_man

VIP Member
You also should consider efficiency. The 80 Plus qualification has made it easy to determine the efficiency of the PSU under load.
 
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