Hi all,

I have a question regarding 12V rail power distribution, and will use the following 2 PSUs as examples:


This one shows 19A on the 12V output.


This one shows 70A on the 12V output.

I'm fully aware the Ultra X3 provides nearly twice the power, but that isn't what this post is about.

Is the CM PSU adequate to power, for instance, a single 8800GT? I ask because 8800GTs are supposed to require around 26A on a single 12V rail, which is more than the CM's 19A per rail.

The bigger question is, how do PSUs distribute their power? Some PSUs (like the CM 550W) have each rail rated at a certain current. Is it safe to assume that these currents can be added to feed a component off a single 12V rail? Other PSUs (like the Ultra 1000W), show one rating for the entire 12V output, despite physically having several 12V cables.

How does it work? I've mined around the Internet a lot but have found many conflicting answers.

Thanks!
- Koraxen

They distribute power exactly how that sticker says..

if that ultra PSU does 70amps at 12volts, thats 840watts soley to the 12v
on the +5v line your lookin at 140watts
3.3 has 79.2 watts

That totals at 960watts

Then factor in the -12v doing 0.8 amp 5VSB doing 15watts


Also that other CM PSU should be perfectly capable as it has 3 seperate 12 rails... which actually is supposed to help with efficiency and consistency

Thanks for the reply.

So you're saying that the CM PSU can power a 12V component that requires more than 19A? The way I initially interpreted the CM sticker was that each 12V rail is limited to outputting a maximum of 19A. This is the main uncertainty I'm trying to clear up. I don't know if in the event of a rail exceeding 19A, that rail would "borrow" more current from another rail's capacity?

it appears that the first PSU has 3 Different 12v rails

No you are right the power supply kinda combines them... I know this post is old but i dont see an answer. If you look at tigerdirects website about the 8800gt youll see this...

http://www.tigerdirect.com/applications/Se...&CatId=3670

1GB of system memory
CD-ROM drive
50MB of available hard disk drive space for basic driver installation
Microsoft Windows XP operating system
PCI Express-compliant motherboard with one vacant PCI Express x16 slot
450W PCI Express-compliant system power supply with a combined 12V current rating of 30A or more.

So as I read it you add up the rails to get the total power output. I sure hope so cuz my OCZ power supply is rated at 18a each on 4 rails and it is expected to power my 8800gt alpha dog so I think you should be good dude