blastingcap
Diamond Member
Consumers often unnecessarily buy large PSUs. Very few people need huge PSUs, and the efficiency curve kills you once you slide below 10% of rated wattage, so your PC idling at 40 watts is getting inefficient electricity, AND you pay $$$ for the privilege of having a 1200W rating that you will likely not use.
Keep in mind a few things:
1) How many amps on the 12v rail is the only thing that matters in a modern PSU. Forget about total wattage. I was using a 450W PSU with up to 37 amps (444W) on the 12v rail to power a system that included such power-hungry components as a stock 1055T (six core Phenom II @ 2.8, higher with Turbo) + moderately oc'd 7970 + four HDDs + DVD-RW drive, 8GB DDR3-1600 RAM @ 1.5v, and a bunch of fans. You couldn't do that with a crappy 450W PSU because a crappy PSU would have a lot less than 444W available on the 12v rail. By the way, I bought the 450W PSU before Anandtech reviewed it, but I wasn't surprised when I later saw that it won Anandtech's Editor's Choice award: http://www.anandtech.com/show/5698/rosewill-capstone-450w-and-650w-80plus-gold/6
2) The CPU + GPU consume most of the 12v rail wattage but RAM, mobos, CPU and case fans, HDD/SSD/optical drives, sound cards, and a few other things draw from the 12v rail as well. If you sum all of those components' peak wattage, it can actually get surprisingly high (over 50W, which is higher than some CPU's TDPs), especially with high-end mobos and overclocked and overvolted RAM.
3) Summing up all the TDPs of a system overstates actual peak consumption, because it's unlikely that everything peaks at the same time. (However, oc'ing that raises power consumption, so account for that.)
4) Efficiency is usually highest at the midpoint of a PSU's rating. E.g., a 500W PSU is most efficient at 250W. But note that most people's PCs are idling more than anything else, so it's usually better to buy the bare minimum necessary to power your system, in order to extract maximum efficiency.
5) Capacitors do age slowly, dragging down the actual continuous max wattage of a unit, but...
6) ...with each die shrink we see higher and higher perf/watt, the net effect being that peak system wattage is on the decline (stock vs. stock). On the CPU side we get slightly better performance each year and significantly lower wattage. On the GPU side it depends on the generation but recently we have seen a much higher gain in performance each year (compared to CPU gains), at the same wattage as previous-generation GPUs. Low-voltage RAM has driven power consumption down, but we also have more RAM so that kind of evens out. Motherboards are dropping in wattage as many of their previous components are absorbed by the CPU--the northbridge and southbridge are shadows of their former selves, and you don't even need as much VRM and power circuitry for the CPU anymore, since CPU wattage keeps dropping. Fans aren't getting any more efficient, but most only use a fraction of a watt anyway. I don't know about optical drives, but hard drive power usage keeps dropping as well, if we even use HDDs anymore because some of them are being replaced by even-lower-wattage SSDs which draw less than a watt at idle.
Bottom line: buy the smallest wattage PSU you can find that still meets your needs on the 12v rail and isn't too loud, enjoy the higher efficiency and savings in your wallet, and let time take care of the rest. Die shrinks will more than counter the effects of aging capacitors.
Keep in mind a few things:
1) How many amps on the 12v rail is the only thing that matters in a modern PSU. Forget about total wattage. I was using a 450W PSU with up to 37 amps (444W) on the 12v rail to power a system that included such power-hungry components as a stock 1055T (six core Phenom II @ 2.8, higher with Turbo) + moderately oc'd 7970 + four HDDs + DVD-RW drive, 8GB DDR3-1600 RAM @ 1.5v, and a bunch of fans. You couldn't do that with a crappy 450W PSU because a crappy PSU would have a lot less than 444W available on the 12v rail. By the way, I bought the 450W PSU before Anandtech reviewed it, but I wasn't surprised when I later saw that it won Anandtech's Editor's Choice award: http://www.anandtech.com/show/5698/rosewill-capstone-450w-and-650w-80plus-gold/6
2) The CPU + GPU consume most of the 12v rail wattage but RAM, mobos, CPU and case fans, HDD/SSD/optical drives, sound cards, and a few other things draw from the 12v rail as well. If you sum all of those components' peak wattage, it can actually get surprisingly high (over 50W, which is higher than some CPU's TDPs), especially with high-end mobos and overclocked and overvolted RAM.
3) Summing up all the TDPs of a system overstates actual peak consumption, because it's unlikely that everything peaks at the same time. (However, oc'ing that raises power consumption, so account for that.)
4) Efficiency is usually highest at the midpoint of a PSU's rating. E.g., a 500W PSU is most efficient at 250W. But note that most people's PCs are idling more than anything else, so it's usually better to buy the bare minimum necessary to power your system, in order to extract maximum efficiency.
5) Capacitors do age slowly, dragging down the actual continuous max wattage of a unit, but...
6) ...with each die shrink we see higher and higher perf/watt, the net effect being that peak system wattage is on the decline (stock vs. stock). On the CPU side we get slightly better performance each year and significantly lower wattage. On the GPU side it depends on the generation but recently we have seen a much higher gain in performance each year (compared to CPU gains), at the same wattage as previous-generation GPUs. Low-voltage RAM has driven power consumption down, but we also have more RAM so that kind of evens out. Motherboards are dropping in wattage as many of their previous components are absorbed by the CPU--the northbridge and southbridge are shadows of their former selves, and you don't even need as much VRM and power circuitry for the CPU anymore, since CPU wattage keeps dropping. Fans aren't getting any more efficient, but most only use a fraction of a watt anyway. I don't know about optical drives, but hard drive power usage keeps dropping as well, if we even use HDDs anymore because some of them are being replaced by even-lower-wattage SSDs which draw less than a watt at idle.
Bottom line: buy the smallest wattage PSU you can find that still meets your needs on the 12v rail and isn't too loud, enjoy the higher efficiency and savings in your wallet, and let time take care of the rest. Die shrinks will more than counter the effects of aging capacitors.
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