Are you planning to run anything else off that PSU aside from the GPU? 
 
The GPU alone will be just fine.  450w is well under 750w.

Jack-Rabbit
cdrom - not really used
3 HDD, 1SSD and 2 - M2 drives

 
Is this one of those new CPU-less PC's I've been hearing about?  Very cool.

750w is minimum for a RTX 3090, if you want to overclock, I'd suggest a 850w or 1000w PSU... otherwise that Corsair HX750i would do just fine.
 
Source:
https://www.guru3d.com/articles_pages/geforce_rtx_3090_founder_review,7.html
 
 

kevinc313

Jack-Rabbit
cdrom - not really used
3 HDD, 1SSD and 2 - M2 drives

 
Is this one of those new CPU-less PC's I've been hearing about?  Very cool.

no I have a 3800x ryzen, should of stated that. Funny how nvidia says 750 for all their 30 series.

You'll more than likely be fine.  I watched a youtube video of a SFF builder who was using corsairs SF600 and it was fine.  This was with a 3080 though. Still close enough for comparison.
 
What Video card do you have now?  I know my 1080Ti uses around 260w at 100% gaming load.  So I could for instance use a Kill O Watt and just add 100 watts for a 3090 than do a little math for efficiency than I would know what my system will require from my PSU.
 
I think most systems will be pulling around 550 from the wall with a 3090 and a reasonably OCd CPU.
 
I like to overspec my PSUs a little though it keeps them running in their quiet modes.
 
 
 
 

kevinc313
Are you planning to run anything else off that PSU aside from the GPU? 
 
The GPU alone will be just fine.  450w is well under 750w.

Well, probably the rest of the PC.

It really just depends on the rest of your build.
There's a bunch of power supply configurators out there where you can plug in your components and get a decent idea of where you'll be.
In my particular use case... I'm running a 3900x on the Aorus x570 Xtreme with 64 gig or Micron B-die *Yes Micron, not the good stuff* @3533 Mhz Cl 16, 18, 18, 36 with 1.38 volts to the rails. (Let's say around 300 watts for the main board, ram, and CPU under heavy load. 330 to be safe.), two fourth gen M.2's (Around 24 watts if both are running at 100%) 3 monitor outputs (negligible consumption) about 12 USB peripherals (Let's say around 40 watts for those three things. That's around 7 watts more than what I need but headroom is a good thing.) two D5 pumps (around 40 watts), 6 140mm Noctuas (about 10 watts total at max) A couple of 120mm fans (about 3 more watts) a large 200mm fan (3 watts).
 
So let's add all that up.
330
+40
+40
+10
+3
+3
=426 watts.
+ the GPU... which could be close to 400 watts if I decide to OC the thing and I'm looking at a possible 826 watts

That means I should probably have a 1000 watt power supply.

Which is what I have. :)

It's better to do the math, or at least use something like a configurator.
https://www.evga.com/power-meter/
https://seasonic.com/wattage-calculator

Jacob.jenson6
It really just depends on the rest of your build.
There's a bunch of power supply configurators out there where you can plug in your components and get a decent idea of where you'll be.
In my particular use case... I'm running a 3900x on the Aorus x570 Xtreme with 64 gig or Micron B-die *Yes Micron, not the good stuff* @3533 Mhz Cl 16, 18, 18, 36 with 1.38 volts to the rails. (Let's say around 300 watts for the main board, ram, and CPU under heavy load. 330 to be safe.), two fourth gen M.2's (Around 24 watts if both are running at 100%) 3 monitor outputs (negligible consumption) about 12 USB peripherals (Let's say around 40 watts for those three things. That's around 7 watts more than what I need but headroom is a good thing.) two D5 pumps (around 40 watts), 6 140mm Noctuas (about 10 watts total at max) A couple of 120mm fans (about 3 more watts) a large 200mm fan (3 watts).
 
So let's add all that up.
330
+40
+40
+10
+3
+3
=426 watts.
+ the GPU... which could be close to 400 watts if I decide to OC the thing and I'm looking at a possible 826 watts

That means I should probably have a 1000 watt power supply.

Which is what I have. :)

It's better to do the math, or at least use something like a configurator.

Thanks for the info.

JayManB

Jacob.jenson6
It really just depends on the rest of your build.
There's a bunch of power supply configurators out there where you can plug in your components and get a decent idea of where you'll be.
In my particular use case... I'm running a 3900x on the Aorus x570 Xtreme with 64 gig or Micron B-die *Yes Micron, not the good stuff* @3533 Mhz Cl 16, 18, 18, 36 with 1.38 volts to the rails. (Let's say around 300 watts for the main board, ram, and CPU under heavy load. 330 to be safe.), two fourth gen M.2's (Around 24 watts if both are running at 100%) 3 monitor outputs (negligible consumption) about 12 USB peripherals (Let's say around 40 watts for those three things. That's around 7 watts more than what I need but headroom is a good thing.) two D5 pumps (around 40 watts), 6 140mm Noctuas (about 10 watts total at max) A couple of 120mm fans (about 3 more watts) a large 200mm fan (3 watts).
 
So let's add all that up.
330
+40
+40
+10
+3
+3
=426 watts.
+ the GPU... which could be close to 400 watts if I decide to OC the thing and I'm looking at a possible 826 watts

That means I should probably have a 1000 watt power supply.

Which is what I have. :)

It's better to do the math, or at least use something like a configurator.
https://www.evga.com/power-meter/
https://seasonic.com/wattage-calculator

I'm not doubting you but have you actually hooked a kill o watt up to your system to see how much power you're pulling.  I think you would be suprised to see its much less than 800W.
 
 

Yeah, a lot of those numbers look pretty high.

Realistically there's no reason nowadays to have a >1000W power supply unless you're building something so absurd you'd have unlimited budget and buy a 1600W PSU anyways.  Vast majority of builds would "survive" on 550W and be perfectly fine at 650W.  
 
Components just aren't as hungry as they once were and SLI isn't a thing.  Also NV clamped down on voltage ceilings...back in the 680 Lightning days I was able to get 2 of them to draw 1300W from the wall...f-ing nuts.
 
Also....older and crappier power supplies may have really low current limited power rails.  Had an XFX / Seasonic one years ago that was 1200? W but if you exceeded 20A on the PCIE plug it would click off.  They lied in the specs about it being single rail.

AnonymousGuy
Realistically there's no reason nowadays to have a >1000W power supply unless you're building something so absurd you'd have unlimited budget and buy a 1600W PSU anyways.  Vast majority of builds would "survive" on 550W and be perfectly fine at 650W.  
 
Components just aren't as hungry as they once were and SLI isn't a thing.  Also NV clamped down on voltage ceilings...back in the 680 Lightning days I was able to get 2 of them to draw 1300W from the wall...f-ing nuts.
 
Also....older and crappier power supplies may have really low current limited power rails.  Had an XFX / Seasonic one years ago that was 1200? W but if you exceeded 20A on the PCIE plug it would click off.  They lied in the specs about it being single rail.

For a single GPU I agree one would not need a KW sized power supply. On the other hand using a 'survivable' level of PSU... not even sure what that is. However, PSUs run most efficient when loaded at ~50% of their rated capacity. There is no practical reason to not take your maximum expected load, double that and call it a day. (if you can't afford the level of PSU you should have, rethink your priorites)

R3L3NTL3SS

JayManB

Jacob.jenson6
It really just depends on the rest of your build.
There's a bunch of power supply configurators out there where you can plug in your components and get a decent idea of where you'll be.
In my particular use case... I'm running a 3900x on the Aorus x570 Xtreme with 64 gig or Micron B-die *Yes Micron, not the good stuff* @3533 Mhz Cl 16, 18, 18, 36 with 1.38 volts to the rails. (Let's say around 300 watts for the main board, ram, and CPU under heavy load. 330 to be safe.), two fourth gen M.2's (Around 24 watts if both are running at 100%) 3 monitor outputs (negligible consumption) about 12 USB peripherals (Let's say around 40 watts for those three things. That's around 7 watts more than what I need but headroom is a good thing.) two D5 pumps (around 40 watts), 6 140mm Noctuas (about 10 watts total at max) A couple of 120mm fans (about 3 more watts) a large 200mm fan (3 watts).
 
So let's add all that up.
330
+40
+40
+10
+3
+3
=426 watts.
+ the GPU... which could be close to 400 watts if I decide to OC the thing and I'm looking at a possible 826 watts

That means I should probably have a 1000 watt power supply.

Which is what I have. :)

It's better to do the math, or at least use something like a configurator.
https://www.evga.com/power-meter/
https://seasonic.com/wattage-calculator

I'm not doubting you but have you actually hooked a kill o watt up to your system to see how much power you're pulling.  I think you would be suprised to see its much less than 800W.
 
 

Yeah, a lot of those numbers look pretty high.

Ya think?
That's 348 watts peak on the GPU.
 

HeavyHemi

AnonymousGuy
Realistically there's no reason nowadays to have a >1000W power supply unless you're building something so absurd you'd have unlimited budget and buy a 1600W PSU anyways.  Vast majority of builds would "survive" on 550W and be perfectly fine at 650W.  
 
Components just aren't as hungry as they once were and SLI isn't a thing.  Also NV clamped down on voltage ceilings...back in the 680 Lightning days I was able to get 2 of them to draw 1300W from the wall...f-ing nuts.
 
Also....older and crappier power supplies may have really low current limited power rails.  Had an XFX / Seasonic one years ago that was 1200? W but if you exceeded 20A on the PCIE plug it would click off.  They lied in the specs about it being single rail.

For a single GPU I agree one would not need a KW sized power supply. On the other hand using a 'survivable' level of PSU... not even sure what that is. However, PSUs run most efficient when loaded at ~50% of their rated capacity. There is no practical reason to not take your maximum expected load, double that and call it a day. (if you can't afford the level of PSU you should have, rethink your priorites)

Survivable meaning if you run p95 and furmark together (which is never going to happen in real world anyways outside of a folding machine or heavily trafficked server), it's not going to over-current the PSU.
 
Practically there's so little price difference between a 550W and a 750W power supply that I'd probably by default get a 650/750W and call it good unless I knew I had plans for top end, heavily overclocked hardware. Maybe upsize if targeting a silent PSU that has some sort of 0rpm fan <50% utilization.

HeavyHemi
Edit, finally I'd like to add this should be looked at two different ways IMO, is the question is my current PSU adequate, or is the question, what PSU should I purchase.

Hmmm .. that'd likely open a can of worms. Adequate is going to vary on what someone intends to do with their system. Personally, I'll spend an hour or so OCing my CPU, less than that on memory and about the same on my GPU. Is that average or below average? Given where we're having this discussion I'd guess it's probably less time than most people here spend on OCing their system so adequate for me may be very, very different than "most" people.
 
It might be better to just ask what components they have in their system, how old is the PSU and what their goals are for the build.

JayManB

Jacob.jenson6
It really just depends on the rest of your build.
There's a bunch of power supply configurators out there where you can plug in your components and get a decent idea of where you'll be.
In my particular use case... I'm running a 3900x on the Aorus x570 Xtreme with 64 gig or Micron B-die *Yes Micron, not the good stuff* @3533 Mhz Cl 16, 18, 18, 36 with 1.38 volts to the rails. (Let's say around 300 watts for the main board, ram, and CPU under heavy load. 330 to be safe.), two fourth gen M.2's (Around 24 watts if both are running at 100%) 3 monitor outputs (negligible consumption) about 12 USB peripherals (Let's say around 40 watts for those three things. That's around 7 watts more than what I need but headroom is a good thing.) two D5 pumps (around 40 watts), 6 140mm Noctuas (about 10 watts total at max) A couple of 120mm fans (about 3 more watts) a large 200mm fan (3 watts).
 
So let's add all that up.
330
+40
+40
+10
+3
+3
=426 watts.
+ the GPU... which could be close to 400 watts if I decide to OC the thing and I'm looking at a possible 826 watts

That means I should probably have a 1000 watt power supply.

Which is what I have. :)

It's better to do the math, or at least use something like a configurator.
https://www.evga.com/power-meter/
https://seasonic.com/wattage-calculator

I'm not doubting you but have you actually hooked a kill o watt up to your system to see how much power you're pulling.  I think you would be suprised to see its much less than 800W.
 

+1 
 
With all due respect, those numbers are completely off and overkill.  My system is similarly complex, if not more and maxs around 600w, maybe 650w, not always but once in a while dependent on load.  Gaming and folding has me on average 450w-550w.  If I had two GTX 480w (Fermi) running furmark, i'd be sitting around 900-950w.  This isn't the case here.
 
750w should be more than enough.  Stick with a platnium or titanium rated PSU and Gold if you're on a budget.