EVGA RTX 3090 FTW3 ULTRA Specs
• Minimum of a 750 Watt power supply
• Three available 8-pin or 6+2pin PCIe power dongles
• Total Power Draw : 350 Watts
 
A 650W unit may be okay for the time being, depending on whether your current PSU has the required PCIe power connectors, and your system wattage need which you can estimate using the OuterVision Power Supply Calculator.

I'm going with an 800w to make sure I have enough headroom for overclocking a 10900k and 3090 in a custom loop.

PSUs are overpriced today because they are not being produced in the right numbers which makes inventory much lower thus exasperating the cost issues.  Not sure why.  I do not buy 80 plus gold or 80 plus bronze units anymore.  I like 80 plus titanium, but will do an 80 plus platinum depending on the build.  I have gotten better overall performance, longer life and feel I get the additional value from the extra cost.  Not saying gold or bronze PSUs are bad at all, but I have historically gotten less time from the ones I have purchase than the higher rated units.  It‘s a personal choice.

Time to upgrade to 750W minimum.

Overclocking a 10900K and a 3090 you will want an 850  or better ideally.  Ive observed a peak power draw from the wall of 650 watts on my overclocked 10900k 1080ti system.  With an overclocked 3090 pulling around 100-200 watts more than my 1080ti I would say 850 is the bare minimum for sufficient headroom.  Most loads wont max out the cpu and gpu at the same time though, the one that really does is flight simming in VR which is what I built my system for.  I would imagine some rendering or video encoding workloads might put a similar strain on your system, maybe streaming too?

Pilot 53

Grey_Beard
PSUs are overpriced today because they are not being produced in the right numbers which makes inventory much lower thus exasperating the cost issues.  Not sure why.  I do not buy 80 plus gold or 80 plus bronze units anymore.  I like 80 plus titanium, but will do an 80 plus platinum depending on the build.  I have gotten better overall performance, longer life and feel I get the additional value from the extra cost.  Not saying gold or bronze PSUs are bad at all, but I have historically gotten less time from the ones I have purchase than the higher rated units.  It‘s a personal choice.

Yeah, everybody always likes to say the cost savings from the efficiency increase wont make much noticeable difference, but thats not why I buy titanium or platinum psu's.  The build quality of the platinum psu's are what makes them worth it.  To get that level of efficiency they are forced to use the best components and circuit design so those psu's often have the best ripple suppression, transient and cross load performance numbers as well as long lifespan due to the high end components used. 

Comparing across the same platform, Gold usually performs better than Platinum and Platinum usually performs better than Titanium.  Because less sacrifices need to made for efficiency.  IMHO and per reviews.

From my own personal experience, the one thing you dont want to cheapen out on is the psu.