PSU power rating clarification

[pravarth]

I'm a bit confused by the PSU power and efficiency rating given by manufacturers. I'm building a new system and I'm not able to choose the correct wattage required.

 

My specs:

Intel i7 3770k with a hyper 212 cooler, so wont oc much. Will try to reach 4GHz

asrock z77 extreme 4 motherboard

2x8gb 1600MHz crucial ballistix ram

powercolor AMD 7870 myst (tahiti le).

samsung 840 128gb ssd and a 1tb seagate drive which i already have for storage

A few fans, still havent decided the case.

 

The gpu has 2 6pin power connectors so can draw a maximum of 225W and according to the anandtech review the cpu should consume about 130W at load. With another 50W for all other components, it comes up to around 400W. I will be using this machine for 3d rendering as well as play games so i will be reaching peak power usage quite often.

 

I'm looking at 3 PSUs: Seasonic s12ii 520W or 620W or corsair tx 650W (which i've heard is a rebranded seasonic s12 )

All of these power supplies are 80plus bronze, so it runs at 85% efficiency. 

 

My question is when a manufacturer says 520W with 85% efficiency, do they mean they can only deliver 442W? or is 520W including the inefficiencies? 

[Guest]

No, it means that what it's drawing from the wall and converting into DC power is at that efficiency. A PSU will draw more AC power than it outputs in DC power due to a loss durring conversion. 

 

Those numbers mean that it is rated at that total output across the 12V, 3.3V and 5V rails. 

[pravarth]

In that case i think 520W should be enough?

[Wats]

In that case i think 520W should be enough?

A seasonic 520 would be perfect for the specs you listed.