I'm currently deciding which parts to put in my new rig and I've got a question about PSU's and how efficiency affects the monthly bill.
I'm looking at the Corsair (enthusiast series) TX650 v2 which is rated as an 80 plus bronze power supply (costs the equivalent of 118$)
and the Corsair CMPSU-650HXEU which is rated as an 80 plus gold power supply and has modular cables (costs the equivalent of 140$)
I obviously can't tell the future but I think I'll use my system for 2-3 years. My computer is running quite a bit most days (6 hours-ish)
but more than half of the time is spent on browsing and idling.
So...is it worth spending the extra juice on getting a more efficient PSU?
Without knowing the full specs of the system, it's hard to say which PSU would be better. There is a chance you may not need a 650W. Between the two listed, however, I would go with the CMPSU-650HX. I like modular PSU's myself because it's easier to keep a case clean.
rest of the system is going to be something like intel core i5 2500k which I plan to do some light/moderate overclocking with. Likely a 6950 or 560 ti which may get some tweaking as well. I'll only be using a single hdd at first but I might throw in an sdd eventually. 4 GBs of ram at first and possibly 8 GBs later.
Lets do some quick math based on those, assuming you are pulling about 350W from the PSU(that will be pretty close to your peak draw for that system) and the power supplies barely clear their respective 50% requirements of 85% for the TX and 90% for the HX then the 650TX will pull 411.8W from the wall, while the HX pulls 388.9W, a difference of 22.9W between them, thats not much. Here power is about 15 cents/kWh, if you were to have the system running at max power 24/7 365 the HX would save you about $30 over the course of the year, realistically we are talking more along the lines of $5-10 per year so it will take a while to make up the price difference.
At lower power numbers the percentage difference will be greater but the absolute power difference will be less so even though the HX650 will draw less in idle situations, a difference of 2W doesnt make much difference.