Power Supply Question

[axehead15]

Just out of curiosity, why do power supply companies say the max power is 550w (for example), when it only puts out 400w?

 

[AMD Radeon]

some crap PSU cant provide stable power for long term at certain point. thats why max 550W

 

[manofchalk]

Because to people who don't know what their doing, a bigger number is better.

Typically they are fairly horrible units, you'l notice in the product code that there will never be a "W" after the number as that definitely means that it can output that amount of Wattage. This also applies to 80+ Certification as well, it will either have 80 in the name or in the specifications will say "up to 80% efficiency" to imply 80+ Certification while it will never explicitly state that it does.
Also some less reputable companies will take the combined wattage of all the rails and use that as the advertised wattage, rather than just the 12v rail wattage which is what really matters.

Example A.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817152028
Says 530W in the title, but from the 12v rails (more on that later) there's only 444W available. If you include the 3.3v rail (meant for HDD's) it comes to 536W in total.
Also a little red switch on the back of the PSU isn't a good sign either, means it doesn't have Active PFC, which is a fairly basic standard among PSU's now.
Up to 80% efficient in the specifications, which means absolutely no 80+ Certification. 80+ Certification also covers acceptable levels of voltage ripple as well, so potentially the PSU could degrade your components as you have no idea how stable the voltages are.
"Dual 12V output circuits provide added system stability" :lol:. That's a fair bit of crock, means that if you were to have too much power draw from the one rail it would burn out, despite that in total wattage it could support it. Getting a PSU with a single 12v rail is best, as then you don't have to concern yourself about which rail is having how much drawn.

Might seem like I picked that PSU and then wrote the first paragraph, but I really didn't.

 

[axehead15]

Thanks for helping me understand this. Now I can help people better!