1000W PSU is the ideal for this combo, and enough for future upgrade. For example Corsair RM1000e or RM1000x.

I have been building high-end rigs for over a decade but unfortunately the power supply situation for these newer flagship parts has been pretty disappointing. My experience with two units that were supposed to be top-tier was not as good as expected once I actually put them under load with my NVIDIA GeForce RTX 4090.

• Be very careful with the 12VHPWR cables because many are still way too stiff. I had issues with a connector nearly melting because it wouldnt sit flush in the socket.
• Avoid older stock that isnt natively ATX 3.0 or 3.1. The transient spikes on these new cards will trip the OCP on older designs even if they claim to be 1000w or more.
• Listen for coil whine before your return window closes. Some of these premium units buzz like a nest of bees once the AMD Ryzen 9 9950X starts drawing serious power. Honestly it is a headache dealing with this lately... just dont assume a high price tag means it will actually handle the power spikes properly without checking the specs first.

I think a 1000W PSU is enough.

Corsair RM1000e

Whatever PSU you choose, make sure it's at least 80+ Gold certified, but preferably Platinum or Titanium for better efficiency. Also, stick to well-known brands with good reputations for quality and customer service. A PSU is not a component to cheap out on, especially with high-end hardware like the 9950X and RTX 4090.

1000W or 1200W 80 plus Gold PSU is recommend.