Ngl, you definitely want ATX 3.0 for the native 12VHPWR support. I recommend 1200W for the extra headroom. The Seasonic VERTEX GX-1200 1200W 80+ Gold ATX 3.0 is a beast with great ripple suppression and stability. Alternatively, the Corsair RM1200x Shift 80 PLUS Gold ATX 3.0 uses a side-connector layout that makes building way easier, tho it requires a wide case. Both handle 4090 transient spikes perfectly.

Tbh, definitely go with an ATX 3.0 unit. Using adapters for a 4090 is just asking for a cable management nightmare and extra points of failure you dont need on a dream build. Regarding the wattage, 1000W is technically enough for gaming, but if you start pushing that i9-13900K with heavy workloads while the GPU is maxed, you're gonna be cutting it close. I'd personally aim for 1200W or even 1300W just to stay in the efficiency sweet spot where the fan doesnt even have to spin up much. If you want the absolute best technical performance, check out the MSI MEG Ai1300P PCIE5 1300W 80+ Platinum. It has a dedicated software interface to monitor real-time power draw and digital regulation which is honestly great for peace of mind when youre running high-end gear like this. Another top-tier option if silence is your priority is the be quiet! Dark Power 13 1000W 80+ Titanium. It's easily one of the quietest units out there thanks to the frameless Silent Wings fan and that Titanium efficiency rating. Quick tip: the most important thing isnt just the PSU brand, but making sure you fully seat that 12VHPWR connector until it clicks. Most of the melting issues actually come from the cable being slightly loose or bent too sharply near the header. If you want a sleeper pick that punches way above its weight class in terms of component quality, the FSP Group Hydro Ti Pro 1000W 80+ Titanium is a fantastic alternative too.

This ^