PSU efficiency and average use system wattage

I asked this before as a reply to the previous thread 'What PSU to get?', but I assume it either wasn't approved or was deleted - I guess I should have started my own thread rather than replying.

I've been trying to figure out selecting a PSU for the system I'm currently building (see end of post). I've read that you want to be targeting about 50% load on your power supply at average power draw to hit the sweet spot on the efficiency curve, however - as far as I'm aware - the average power draw of your components is usually significantly lower than their rated power consumption, tdp, or peak power. What kind of a wattage margin do you want to add for safety, and how do you figure out how to nail the sweet spot of the efficiency curve for a given power supply?

I'm not sure whether I've overspecced my system's proposed power supply or not; PC Part Picker estimates the wattage at a little over 350W, though that isn't including the pump of the Asetak 645LT (not in their database). I know that for optimising wattage with respect to the power curve of a PSU, we are talking efficiency gains of a few percent at best, yet I have a compulsion to do it right :laugh: Looking at a calculator like overview, it recommends a 80+ bronze 450W power supply, which feels quite low and quite inefficient - efficiency matters quite a bit to me, because any inefficiency is excess heat dissipated into my case, and it's already going to be a tight squeeze component-wise and thermally in the Dan A4!

Type	Item	Price
CPU	AMD Ryzen 5 5600X 3.7 GHz 6-Core Processor	Purchased For £299.99
CPU Cooler	Asetek 645LT 92mm SFF AIO Liquid Cooler	Purchased For £76.34
Motherboard	MSI MPG B550I GAMING EDGE WIFI Mini ITX AM4 Motherboard	Purchased For £149.99
Memory	Corsair Vengeance LPX 16 GB (2 x 8 GB) DDR4-3600 CL16 Memory	Purchased For £79.99
Storage	Samsung 980 Pro 250 GB M.2-2280 NVME Solid State Drive	Purchased For £84.98
Storage	Samsung 860 Evo 1 TB 2.5" Solid State Drive	Existing Component
Video Card	Gigabyte GeForce RTX 3070 8 GB EAGLE OC Video Card?	£672.95 @ Overclockers.co.uk
Case	DAN Cases A4-SFXv4.1 Mini ITX Desktop Case	Purchased For £195.44
Power Supply	Corsair SF 600 W 80+ Platinum Certified Fully Modular SFX Power Supply?	£119.87 @ More Computers
Monitor	LG 27GL83A-B 27.0" 2560x1440 144 Hz Monitor	Purchased For £178.00
Monitor	LG 27GL83A-B 27.0" 2560x1440 144 Hz Monitor	Purchased For £178.00
Keyboard	Dell KB212-B Wired Standard Keyboard	Existing Component
Mouse	Logitech MX Ergo Wireless Optical Mouse	Existing Component
Speakers	Logitech Z200 0 nW 2.0 Channel Speakers	Existing Component

You're fine. While many people do overspec their PSU, by going platinum you're ensuring that efficiency at low loads is still OK.

Personally i'd pay the extra £10-15 and get the 750w version, iv'e got a Project 7 750w Platinum rated PSU and thats not enough for a 3070 as at peak draw it shuts down the PSU, might be different with a normal GPU as mine is the FE which draws it all from MB and one 8pin connector.

Quote:

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Originally Posted by Jasp

Personally i'd pay the extra £10-15 and get the 750w version, iv'e got a Project 7 750w Platinum rated PSU and thats not enough for a 3070 as at peak draw it shuts down the PSU, might be different with a normal GPU as mine is the FE which draws it all from MB and one 8pin connector.

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Aerocool are not know for making good PSU's but even so, that sounds like the 3070 FE was badly designed and relies on too high a boost to me?

@jasp you've definitely got a defective psu because I'm running a 3060ti FE on a 450w silverstone. Are you sure it's the psu and not an unstable cpu voltage or memory overclock etc? A 3070 should not draw much more than 220w even at peak.

The card pulls over 230w at times from the Nvidia overlay information at which point it shuts the system down, which is above the 225w provided by the slot and 8 pin, at the moment iv'e got it undervolted to keep it under 200w which works well.

Quote:

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Originally Posted by Jasp

The card pulls over 230w at times from the Nvidia overlay information at which point it shuts the system down, which is above the 225w provided by the slot and 8 pin, at the moment iv'e got it undervolted to keep it under 200w which works well.

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Ah fair enough, that sounds like very poor design on nvidia's part. Ridiculous if you think about it that they would under spec their FE like that. I wonder how many people are suffering with that and unaware of the problem.