Based on that review it's not something I would go out and buy, but it's not something that I would go out and replace if I already had it, unless you are having specific problems with it.
Obviously the voltage regulation could be better but it is in spec.
It certainly has enough power for a system with two 5850s. The distribution of the 12V rails doesn't look like it's a problem either.
I agree with Silvune your psu should be fine to power another 5850.
Cougar actually have about 7/8 different 700W PSUs, so it would be helpful to know which model Mokkalokka has.
Thanks for the replies. Well, the thing is that I bought my computer as a final product - so I do not know the specific details about the PSU, other than the ones I wrote. How would I be able to check what model I have in my machine?
You would have to open the case up and try to find the label on the PSU.