150/0.9 = 166.66W (90% efficiency of small PSU)
150/0.85 = 176.47W (85% efficiency of big PSU, -5% worse according to the numbers provided before)
30/0.9 = 33.33W (90% efficiency of small PSU)
30/0.75 = 40W (75% efficiency of big PSU, -15% worse according to the numbers provided before)
And well, if you run your PC a lot, every watt counts. 7W / 1000 * 365 days * 24 hours = 61,32 kWh used up by that 7W difference through a year when computer runs 24/7. In my case when the price per kWh is 0.135156€/kWh equals to 8.28€ saved in one year - so i can have one more good lunch at restaurant
. Do your math this way (power difference / 1000 * average number of days computer is used in year * average number of hours computer is used in day when it is on) and you will get your power consumption difference, multiply it by your kWh rate and you will see how much more you pay.
Excellent computations there!
I'm not as frugal, though, and pay top dollar for all the components, generally, an extra $20/year is as unto nothing in my mind.
But in any case, I went out and bought a fanless SeaSonic as per the above (520W model, tho', in case I someday want more oomph).
Of course, this is going into a Corsair Obsidian 550D, which has bad airflow and the PSU is mounted on the bottom (which has 2 vents to vent fanned PSUs immediately), so I have worries the rising heat from this fanless model will have nowhere to do and pool around the CPU, which ain't good.