PSU for SFF PC: ATX vs. SFX vs. SFX-L vs. DC-DC

Coolio

n00b
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Jan 8, 2021
Messages
52
Hey guys,

I'm a first-time SFF PC builder so your comments will be very appreciated. :)

My build will be based on the following components:
  • Case: Dan A4 (7.2L) or Louqe Ghost S1 (8.2L) or FormD T1 (9.5L)
  • CPU: AMD Ryzen 5600X (65W) or 5800X (105W)
  • GPU: Nvidia GeForce GTX 1070 (150W) or RTX 3070 (220W)
  • MoBo: B550 (5W) or X570 (11W)
  • Other: x1 (possibly x2) SSD; 32Gb RAM, x2-3 fans
So in the very light scenario my overall system TDP will be ~250W, in the very heavy ~370W. Here are the questions I wanted to discuss with you guys:
  1. Am I right I need a 320-350W PSU for the light scenario and a 450-470W for the heavy one?
  2. If I plan to upgrade CPU+GPU once (in 2-3 years) shall the answer to Question #1 be different? That will be the "next gen" upgrade to the similarly positioned CPU/GPU, not that I will go for the very top (or vice versa, the entry level) model.
  3. SFX vs. ATX: pros - smaller size; cons - higher "price for Watt", higher heat generation rate (= extra expenses on cooling solution), higher noise level (due to the smaller fan). Right or wrong? Anything to add?
  4. SFX-L: doesn't make much sense, as though it hypothetically may generate less heat and noise (because of the bigger fan), it ruins the concept itself of the "smaller PSU for a SFF build", being larger than SFX. Am I right?
  5. DC-DC seems to be a good choice: produces no noise/heat, takes minimum space inside the case. Could be more expensive though, but isn't PSU something that one can invest in for years ahead and that will be reasonable?
Thank you for your comments!
 

Tsumi

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Mar 18, 2010
Messages
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1. Yes, a 450 watt PSU is likely sufficient for the upper end of your planned needs.
2. No, it most likely would not be different.
3. Nothing to add.
4. Depends on the case you choose. If your case can accommodate SFX-L while housing everything else, why not use SFX-L. On the other hand, if your case can't accommodate SFX-L then the choice is obvious.
5. Very few studies on the output quality of a DC-DC PSU. You will also have a large external power brick. Pick this only if you want to have the absolute smallest case possible and it doesn't have room for a SFX PSU.
 

Coolio

n00b
Joined
Jan 8, 2021
Messages
52
Tsumi Thank you for this input, appreciate that!

If your case can accommodate SFX-L while housing everything else, why not use SFX-L.
Yeah, I mean it sounds 100% logical, but if the size is more or less the same (is it?) what are the benefits of particularly SFX-L vs. ATX?

Very few studies on the output quality of a DC-DC PSU. You will also have a large external power brick.
Haven't gone that far as studies yet, but what do you mean by quality: stability of the electrical flow, sufficiency of the delivered volume (declared vs. real-life), etc.? All laptops use DC-DC PSUs, so why not spread this approach to desktop, when need is?
Those 3 cases I've mentioned (7.2 - 9.5L) can perfectly accomodate internal PSU, so my interest to DC-DC arises from the desire to 1) decrease noise, 2) offload the cooling and 3) free space for internal airflow.
 
Joined
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If you are planning to go with a 5800X and a RTX 3070, I´d suggest getting a 600W PSU to be on the safe side. TDP is not very reliable nowadays because these components can exceed the advertised TDP when stressed. So you will have a scenario where your PC will shut down when playing a demanding game or running a CPU heavy operation.

Also bear in mind that most PSU have an average 85% efficiency, so in order to supply 100W, it will actually draw around 115W.

Getting the 600W will also give you headroom in case you decide to upgrade and will run cooler with your current setup because it won´t be operating close to the rated limit.
 

Tsumi

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Tsumi Thank you for this input, appreciate that!


Yeah, I mean it sounds 100% logical, but if the size is more or less the same (is it?) what are the benefits of particularly SFX-L vs. ATX?


Haven't gone that far as studies yet, but what do you mean by quality: stability of the electrical flow, sufficiency of the delivered volume (declared vs. real-life), etc.? All laptops use DC-DC PSUs, so why not spread this approach to desktop, when need is?
Those 3 cases I've mentioned (7.2 - 9.5L) can perfectly accomodate internal PSU, so my interest to DC-DC arises from the desire to 1) decrease noise, 2) offload the cooling and 3) free space for internal airflow.

SFX-L is smaller than ATX. There are cases that will fit SFX-L but not ATX.

Quality: Ripple suppression, voltage droop, transient spikes, etc. So yes, stability, sufficiency, everything. No enthusiast cares about laptops because they can't control the configuration, so few, if any, reviews are done, not to mention it is much harder to test.

If you are planning to go with a 5800X and a RTX 3070, I´d suggest getting a 600W PSU to be on the safe side. TDP is not very reliable nowadays because these components can exceed the advertised TDP when stressed. So you will have a scenario where your PC will shut down when playing a demanding game or running a CPU heavy operation.

Also bear in mind that most PSU have an average 85% efficiency, so in order to supply 100W, it will actually draw around 115W.

Getting the 600W will also give you headroom in case you decide to upgrade and will run cooler with your current setup because it won´t be operating close to the rated limit.

Most quality PSUs can handle short surges in load. Additionally, PSUs are rated on the amount of power they can put out, not how much they can take in. A 600 watt PSU can deliver 600 watts.
 
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Most quality PSUs can handle short surges in load. Additionally, PSUs are rated on the amount of power they can put out, not how much they can take in. A 600 watt PSU can deliver 600 watts.

Indeed, but I think playing a demanding game for 2-3 hours wouldn´t classify as a short surge, power draw would vary in certain areas, etc, but overall you are pushing both CPU and GPU to use a lot of power.

At any rate, I still think that it would be ideal to have some headroom if you want to avoid headaches. Unless OP intends to stick with a 5600X and a modest GPU, then I guess 450W would be plenty.
 

Tsumi

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Messages
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Indeed, but I think playing a demanding game for 2-3 hours wouldn´t classify as a short surge, power draw would vary in certain areas, etc, but overall you are pushing both CPU and GPU to use a lot of power.

At any rate, I still think that it would be ideal to have some headroom if you want to avoid headaches. Unless OP intends to stick with a 5600X and a modest GPU, then I guess 450W would be plenty.

RTX 3070 has been measured to draw approximately 220 watts, as stated. Peak draws (not sustained, and will only briefly be seen during gaming) will be 270-300 watts, at best. CPUs rarely ever see peak draws during gaming.
 

Libnok

Weaksauce
Joined
Feb 7, 2021
Messages
108
Hey guys,

I'm a first-time SFF PC builder so your comments will be very appreciated. :)

My build will be based on the following components:
  • Case: Dan A4 (7.2L) or Louqe Ghost S1 (8.2L) or FormD T1 (9.5L)
  • CPU: AMD Ryzen 5600X (65W) or 5800X (105W)
  • GPU: Nvidia GeForce GTX 1070 (150W) or RTX 3070 (220W)
  • MoBo: B550 (5W) or X570 (11W)
  • Other: x1 (possibly x2) SSD; 32Gb RAM, x2-3 fans
So in the very light scenario my overall system TDP will be ~250W, in the very heavy ~370W. Here are the questions I wanted to discuss with you guys:
  1. Am I right I need a 320-350W PSU for the light scenario and a 450-470W for the heavy one?
  2. If I plan to upgrade CPU+GPU once (in 2-3 years) shall the answer to Question #1 be different? That will be the "next gen" upgrade to the similarly positioned CPU/GPU, not that I will go for the very top (or vice versa, the entry level) model.
  3. SFX vs. ATX: pros - smaller size; cons - higher "price for Watt", higher heat generation rate (= extra expenses on cooling solution), higher noise level (due to the smaller fan). Right or wrong? Anything to add?
  4. SFX-L: doesn't make much sense, as though it hypothetically may generate less heat and noise (because of the bigger fan), it ruins the concept itself of the "smaller PSU for a SFF build", being larger than SFX. Am I right?
  5. DC-DC seems to be a good choice: produces no noise/heat, takes minimum space inside the case. Could be more expensive though, but isn't PSU something that one can invest in for years ahead and that will be reasonable?
Thank you for your comments!
I'm actually waiting for the Dan A4-H2O to be released to start my SFF conversion with my B550, 5600x, 3070 that I'm on. I'm currently on an ATX 625w bronze and it has no problem at full load, pulling at most 500w from my UPS with 3 monitors and some other small things. I figured I'd post about it since it was just announced a couple weeks ago.

 

Coolio

n00b
Joined
Jan 8, 2021
Messages
52
Thank you all guys for your valuable comments - highly appreciate your help!

Also bear in mind that most PSU have an average 85% efficiency, so in order to supply 100W, it will actually draw around 115W.
PSUs are rated on the amount of power they can put out, not how much they can take in. A 600 watt PSU can deliver 600 watts.
Good point - on the one hand it's logical to declare what the customer finally gets, on the other - heads up for me to double-check the manufacturer is not cheating. :)

At any rate, I still think that it would be ideal to have some headroom if you want to avoid headaches.
Sure, but I've heard the reserve is to be within +30% of the TDP, while you propose almost to double it. I mean it won't hurt of course, but isn't it an excessive spending?

Peak draws (not sustained, and will only briefly be seen during gaming) will be 270-300 watts
Which PSU-related technologies will you recommend in order to avoid/minimize typical problems (of any kind) the PSU may face? In other words: which PSU technological features do you find crucial/good to have?

I'm currently on an ATX 625w bronze and it has no problem at full load
Is this bronze/silver/gold ranking really worth to pay for? I mean PSUs which really keep to that spec are only available from reliable manufacturers, so at the very least you've bought a quality product. But what about the ranking position - how does it matter in practice? Platinum and Titanium seem to be extra, but Gold looks like a golden (ha-ha) mean for the system with 2-2.5h daily workload, uh?
 

Libnok

Weaksauce
Joined
Feb 7, 2021
Messages
108
Is this bronze/silver/gold ranking really worth to pay for? I mean PSUs which really keep to that spec are only available from reliable manufacturers, so at the very least you've bought a quality product. But what about the ranking position - how does it matter in practice? Platinum and Titanium seem to be extra, but Gold looks like a golden (ha-ha) mean for the system with 2-2.5h daily workload, uh?
I don't think that it's extremely important to worry about the rating. I only mentioned the rating of mine for completion. The PSU that I'm using is probably 10 years old as well, I didn't buy it, it was given to me second hand. I've been using it for almost 5 years in my daily driver.

As for the ratings, I'd say that gold is sufficient for most. Beyond gold there are diminishing returns in regards to price/performance. Of course you could calculate how long the more expensive unit would take to pay for itself. It's just an efficiency rating, so you know at least that they went through the process of qualifying their product. To a lesser extent, it could mean that more quality parts are used which could affect longevity.
 

Tsumi

[H]F Junkie
Joined
Mar 18, 2010
Messages
13,480
Efficiency rating has little bearing on performance, and can easily be cheated. I would never use 80+ ratings in choosing a PSU.

Rather than focusing on technology and buzzwords, look for reputable manufacturers and PSUs reviewed by hardware enthusiasts. https://www.thefpsreview.com/ is a good place to start.
 

Coolio

n00b
Joined
Jan 8, 2021
Messages
52
Thank you guys! I guess makes sense to take the next step and read review, that's right. :)
 

Libnok

Weaksauce
Joined
Feb 7, 2021
Messages
108
Efficiency rating has little bearing on performance, and can easily be cheated. I would never use 80+ ratings in choosing a PSU.

Rather than focusing on technology and buzzwords, look for reputable manufacturers and PSUs reviewed by hardware enthusiasts. https://www.thefpsreview.com/ is a good place to start.
Shameless plug aside. ;) It's sound advice.
 
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