How to interpret wattage sticker on my PSU

[Freddy1765]

I've got an Arctic Cooling Fusion 550.
Review here: http://www.anandtech.com/show/2724/2
For convenience I'll write the numbers on the sticker here:

Continuous Output: 500 W
+12V nr1 : 17 A
+12V nr2 : 17 A
Combined output for the above: 408 W
+5 V: 24 A
+3.3 V : 24 A
Combined output for the above: 130 W
-12V : 0.8 A
+5V SB : 2.5 A

I've read that pretty much everything in a computer runs off of the 12V rails, so does this mean 408 W is basically my power limit?
The reason I ask is I'm upgrading my computer soon, but I'd like to keep my PSU if possible..
According to a review of the GPU I'm looking for (7870) by AT, total system power for that setup was 336 W at the wall. Is it then reasonable to assume the PSU (given 80 % efficiency) has an output of ~270 W?
If so, that's well below my cap and I can safely upgrade, right?

 

[richaron]

Yes 408W, but that's over 2 rails (read the Sticky). If a 7870 draws 175W at load this only leaves ~30W on that particular rail. I don't know how your psu is set up, but you might have to power your optical/hard/ss drives on that same rail.

I don't know how many of those you have... It could well work, but you'd be sailing close to the wind

500W psu pumps out 500, at 80% it will be pulling 625W from the wall.

 

[Freddy1765]

Then how do I connect the GPU/CPU to specific rails?

 

[richaron]

From the Sticky I directed you to:

Typical multiple +12V rail configurations:
2 x 12V rails
Original ATX12V specification's division of +12V rails.
One rail to the CPU, one rail to everything else.
VERY old school since it's very likely that "everything else" may include a graphics card that requires a PCIe connector.
Typically only seen on PSU's < 600W.

I don't know your psu :|

I would guess a new one is on the cards.

 

[Freddy1765]

I'll open it up and have a look around
On a side note: I just noticed the MoBo I intend to buy uses a 4pin ATX connector, (it's a Gigabyte GA-Z68AP-D3); if I end up OC'ing the 2500k I'm getting with it, would a board with an 8 pin be better, or doesn't it matter?

 

[richaron]

You'll should be able to get a mild overclock on anything.

But if you want a larger overclock you'll probly want a motherboard & psu designed to use 8 pin. In theory you'll have more power to play with & more stable power. Boards with 8 pin cpu power could also have better power circuits & an OC friendly BIOS.

 

[Freddy1765]

Alright, thanks dude! I'll check out my other options and think about what the flip to do

 

[richaron]

No probs good luck. Google is your friend

 

[Freddy1765]

And now that I know more specifically what to search for, I'll be using it diligently