I wouldn't have posted it, if I didn't think it was worthwhile. It's not as if I have posted a ton of fluff here.
My suggestion would be to attach a kill-a-watt to a known system, plug in the data, and compare its recommendation to real life. I'll let you be the judge. If it fails then have a moderator remove the thread as spam. I'm not married to it.
As PSU estimators go, it is not too bad; Antec uses it as their calculator.
FYI, the Kill-A-Watt does not play nice with some PSUs, especially ones with APFC. Sometimes it reports values that indicate over 100% efficiency.
Start with a bog-standard cheapish but at least half-decent PSU. If you are not sure what that is, pick it up. If it has no particular weight in your hand, it's decent. If it seems a bit light, it's half-decent. If it seems really light, it's carp - throw it away. Good ones cost real money and are always heavy. There are only four sorts of power supply:
Now, ask yourself ....
1: Does the system have:
Multiple drives (more than three - HDD or DVD, both count)
Large graphics card (needs large heat sink and/or cost over $200 when new)
Large graphics card (as above)
Very power-hungry CPU
Higher than typical reliability requirement
Weird add-on stuff that chews juice
If you answered YES once, you can get away with a CARP PSU but you should have a HALF-DECENT unit.
If you answered YES twice, you can get away with a HALF-DECENT PSU but you should have a DECENT unit.
If you answered YES three times, you can get away with a DECENT PSU but you should certainly consider a GOOD unit.
If you answered YES more than three times, you won't get away with a DECENT PSU, you absolutely must have a GOOD unit.
Note: yes, you ask the graphics card question twice and count the answer twice.
For a while, my off-the-cuff PSU recommendation (for people seeking free advice) goes like this:
Number of physical CPUs+GPUs x 200 = wattage (W)
If W>1200 or using TEC then "That is a specialized application. Do your own research or hire a consultant."
If W <=1000 and buyer has compatible Antec case: Antec CP series PSU
If W >=1000 then Antec TPQ1200 (What, it might be too loud? Do your own research.)
If W<= 1000 then "Pick whichever Corsair PSU you like best rated at W or above."
If "Corsair = $$$" then "You get what you pay for."