Question about power supply

[radiobox]

If I build a system that only require max 400watt and put in 750watt power supply, do my electricity bill be higher compare if switch to 550watt power supply and both of them is rated 80+ gold same brand and model.

 

[Alternative X]

The thing about PSUs is that 80+ efficiency standards only governs PSU efficiency between 20% to 100% of the stated wattage of the PSU (with the exception of 80+ Titanium). PSU efficiency tends to be at the lower end at the 20% mark, peaks at the 50% mark and drops off at 100% due to the increased temperatures in the PSU. However, the differences in efficiency is only about 2% between different loads and thus should not have much impact on your power bill. However, some PSUs are rather inefficient at loads lesser than 20% with an efficiency of about 70+% to 81%, which is why proper PSU review sites also tests PSUs at very low loads.

Hence, you will get a far higher power bill if you run a 150W system with a 1500W PSU due to the inherent inefficiencies at low loads than with a 200W PSU or a 300W PSU and the differences with both 200W and 300W PSUs will be insignificant, assuming that the 200W, 300W and the 1500W PSUs are of the same PSU platform and carries the same efficiency rating.

 

[devilwahaha]

TL;DR, you will probably save about a few dollars a year if you go up to platinum efficiency, so dont bother buying PSU for the rating, unless you're interested in the design and outlook then go ahead.

 

[Godeau]

In layman's term, there is a certain sweet spot where a psu peaks in its efficiency, and that is around 40 ~ 60%. Do note though, it is quite a small, negligible % amount so it does not translate to much more savings overtime because of the initial price you have to pay for a higher wattage psu.

However, it is advisable to try and fit into that range not only for efficiency reasons, but for deteriorating components like capacitors due to prolonged usage and heat which decreases the max output of a psu overtime.

By your example, if I have a pc requiring 400W max, I would probably go for a psu that is around 600~650W.

 

[unhinged_loon]

In layman's term, there is a certain sweet spot where a psu peaks in its efficiency, and that is around 40 ~ 60%. Do note though, it is quite a small, negligible % amount so it does not translate to much more savings overtime because of the initial price you have to pay for a higher wattage psu.

However, it is advisable to try and fit into that range not only for efficiency reasons, but for deteriorating components like capacitors due to prolonged usage and heat which decreases the max output of a psu overtime.

By your example, if I have a pc requiring 400W max, I would probably go for a psu that is around 600~650W.

If you buy a high quality PSU, cap aging is rarely an issue unless you plan to use it for more than 10 years.

Capacitor aging is overblown by half pass six pseudo hardware experts who don't actually know hardware but only repeat myths perpetuated across the internet. People should actually look at cap spec sheets...
Power supplies degrade in power output over time? - jonnyGURU Forums


If a (Delta made) 250W PSU can power a Pentium 4 hotbox for 10 years before failing (failure cause unclear), I'm not going to sweat about caps in a decent quality PSU (not that Deltas are not decent).

However, if you want to use something like this: http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=204

Then upsize all you want...


Secondly, the PC rarely hits the maximum theoretical power draw (estimated based on TDP) even when gaming. It spends most the time drawing <100W unless you are an AMD user.