New PSU

Here is a link to a technical review of the psu:

http://www.overclockersclub.com/reviews/oczsxs600/

The review will answer you questions. Read the section about efficiency.

Thing is that I don't know much about PSUs. I don't when there's a good efficiency when there's not. Review probably won't help me  

Read the conclusion on the last page of the article. It is written in plain English that is easy to understand.

Efficiency is simple. Over 80% = good; under 80% = bad.

I would go higher. Get at least a 700 watt or 800 watt just to be safe.

no offense mamw93 but where are u getting ur numbers?!?
I mean, im not attacking u or anything, but u DONT NEED that sort of power in anything.
I would ask u to do reading b4 posting dud information and confusing posters here

Back to the OPs question, imo its not the best out there...its mediocre. Wont blow up but wont give u great efficiency and compared to others, its performance is not top notch.

Antec Earthwatts 500 or Corsair VX550 would be good choices.

In anything?

I'll fully agree that the OP will be fine with a good quality 500W or so from Corsair or Seasonic (or similar), but there are certainly systems out there that absolutely need 700-800W or more. For example, I have a fairly highly overclocked i7 with a pair of 4870x2s (I just recently added a second  ). That certainly requires more than 650W under full load (though I haven't measured it since adding the second 4870x2).

Well, yes i understand that

But u get my point
I mean, yea if u want to stay in the efficiency sweet spot of 60-80% then get a 850/1000 watt for UR system (or 2 295s)
U could probably run that on a 650 (try the Signature  ) but it would be a very high load :X
But i mean...700/800 for 2 GTS 250s?!

The Signature 650 comes with one PCIE 6+2-pin and one PCIE 6-pin cable. It has the guts to run a pair of high-end cards, but not the cables (without adapters). I think it is intended mostly for either a single high-end card, or for people (like me) who just want the peace-of-mind of having an excellent PSU.

Maybe, but I think the actual draw will be well above 650W full load. I doubt that the Signature 650 could pull it off. I'll test it at some point though, and post the results  

(Oh, and I have a Corsair HX1000W)