I tested total energy consumption by my PC.
No matter what load I applied in the sim (GPU 100%, CPU 40%) I never exceeded 600W.
4090
7800x3D air-cooled
32 GB RAM
22TB NVME
11TB SSD
1*4TB HDD
Probably my 1000W PSU is too big, 850W would be probably enough.
My RTX4090 / 5800X3D uses 500W in Cyberpunk and about 450W in MSFS (just PC not monitor).
I use a 1000W PSU but a good quality 750W would do the job.
One advantage of my 1000W ATX 3.0 PSU is that I can use the 12vhpwr cable that comes with the PSU instead of the octopus adapter that comes with the GPU.
850W Gold P/S
5800X3D
3090 Ti
64GB DDR4
WiFi 6 PCIe card
2 x NVMe
2 x SATA SSD
10 case fans
Closed loop pump/reservoir
32" 4K monitor
2 x iPad
1 x 19" HD monitor
Enough peripheral USB devices to eat 3 x 8-port powered hubs.
According to my UPS, I draw 720W while flying.
Wanna’ trade your 1000W for my 850W? 
It’s only going to draw what it needs. Consider it 400 watts of headroom. Keep the 1000-watt supply.
100% agree.
If its a 1000W power supply, but your system only draws 600-800W, the Power supply will run a lot cooler, and thus last a lot longer.
HEAT is the enemy of Electrolytic Capacitors, which are the components that typically deteriorate in a PSU, eventually leading to instability and poor dynamic regulation, which can lead to CTDs
Extra power isn’t bad. I have a similar setup w/more RAM and a 3090. No issues and I don’t have to worry about stressing the unit.
I know it will work. I posted as advice for the others to save them some cash when building 4090/Ryzen based system.
Another good thing about my 1000W PSU is that the fan doesn’t turn on until 50% load. So less noise and less dust being pulled into the PSU.
PC is using under 500W when playing MSFS (RTX4090 / 5800X3D).
1000W PSU‘s are just a little more expensive than 800W. The diffenrence is rather if you buy a quality product instead of a cheap one. 
Correct-a-mundo.
I have a really basic PC setup for MSFS. Maybe shocking basic for some of you! But it works fine and I can run MSFS smoothly on average settings! I do have a fast internet connection though.
My system basicly: an Intel i5-9500 processor that is consuming 65 watts max, a GTX-1060 Graphics card that is using max 120 watts. Besides that I have 32 GB DDR-4 RAM. I am running on Windows 11 Pro.
My power supply is 300 Watt. It’s enough. I actually measured the power usage of the system and it never exceeds 110 Watts when playing MSFS on average setting (and that’s good enough for me and the framerate is around 60 FPS).
So: even on such a minimum system, and very low power consumtion, it runs fine!
I could not afford more and I am happy I can run MSFS, my old PC was running FSX fine but could not handle MSFS (well it actually had the bare minimum specification for MSFS) . And: my old PC did not meet the ridiculous requirments to install Windows 11
So maybe this is good news for those who just look for a good enough PC on average standards but low costs.