Well, this is a trite, but unfortunately true statement; because they want you to give them your money for their merchandise. Business can be an ugly thing.
"Cooking" the specs is a practice that has been with us for years. Manufacturers have methods to make the customer see exactly what they want them to see and it's a long, no, very long, seamy story. The FTC stepped in with legislation about reporting the power output of an audio amplifier, so that the RMS power claim must be reported. RMS is the same type of measurement (in reverse) that you would use to measure the draw of a light bulb! Basically, if you say that the amp puts out 75 watts, then the POS better damn well light that 75 watt light bulb. period.
The PSU calculator probably needs another couple of tries on your part. Basically tell it what you have, then it'll tell you what you need. Beyond that it's just a question of knowing what components yoy have, so you 'll know what to tell it. At this point, the PSU Calculator, at least for the time being, is moot, since you have all ready purchased your unit. As I mentioned earlier the 600 watt Rosewill will certainly power your system admirably. My crystal ball is on the fritz, and I have no personal experience with that product, so who knows what the future holds.
The only Rosewill product I personally own is an variable speed 120mm case fan, and I suppose it seems nice enough. (Active fan speed control, not just a variable resistor like some).
@Rage; PSUs do have different efficiency ratings @ different demand levels. The issue of sagging output as operating temperatures is another matter. So, both statements (yours and mine) are true. Actually fitting a PSU to a system, I think the ideal is somewhere around 25/30% more than the maximum actual load. That is perhaps the point where deference to temperature rise meets wastefulness.in terms of money and materials. But of course, who knows?
