Too high voltage?

[MadMacs]

I have a question regarding psu's.
if you purchase an 850w psu, but you pc only needs 600w then does your pc only take what it needs or will it always run 850w?

thanks

 

[Dreamcaster]

it will only take what it needs

 

[MadMacs]

Great, thanks for the reply.
But does this mean that an 850w model will be less efficiant then say a 600w model?

and obviously there will be a noice issue right?
(I was looking at the new coolermaster psu)