Why are some PSU calculators iffy?

Here is the correct one from PCPartPicker for my new build rated at 920 watts:

http://pcpartpicker.com/user/cad5359/saved/1LuY Check it out here and voice your opinions also!

And the one at Xtreme PSU calculator here is only rated at 783 watts. Why is it wrong? http://www.extreme.outervision.com/psucalculatorlite.jsp

I tested it on Newegg. Minus all the Corsair fans, the desktop build itself needs at least 730 watts. (minus all the corsair fans. Jesus you're getting a ton, lol)


I'm guessing PCPartPicker is including the monitor, fans, etc

I really dont like those online calculators. For example it will say that a 800w psu is needed. Budget may already be tight so person 'x' goes and buys a $30 pos 800w psu only to build the system. Powers on then 'bang!'. The build quality etc isnt mentioned nor the required amps on the 12v rail. For example Thortech psu's are a relatively expensive psu's that are targeted at gaming rigs. Trouble is their stated ouput is far from ideal and are down right terrible pieces of equipment with bad filtering and high ripple.

Also one must take into account the efficiency range of the psu, if a psu is run close to its maximum output all the time its lifespan will be greatly reduced.

You've chosen a really nice psy there with the 1200i so I'd stick with that, its an amazing piece of gear and will last a long time. It will never be stressed even with everything going balls deep crazy and overclocked. Plus the efficiency of those units is a work of art. Add to that the monitoring software you can then loop with the h100i you'll have yourself a nice rig.