Should I upgrade my PSU before buying an RX 9070 XT?

There’s no technical reason you can’t install the new PSU now, although it may be more convenient to do both upgrades at the same time. Waiting also has some advantages: the warranty and service life of the PSU start running immediately, and better or more efficient GPUs may be available by the time you’re ready. Depending on the age and condition of your current unit, a good 650W PSU may even be sufficient for some future GPU choices.

I’d probably wait and purchase the PSU closer to the graphics card. Power-supply prices and models change, and buying a 1000W unit now could leave you with more capacity than you need later. If you do buy early, choose a high-quality 750W–850W ATX 3.1 model rather than focusing only on the wattage rating.

You can absolutely replace the PSU before upgrading the graphics card, and the new unit will work fine with your current RTX 3050. Just remember that modular PSU cables are not universally compatible. Remove every cable from the old PSU and use only the cables that came with the replacement. The Rosewill model is considered acceptable, but I’d lean toward a reputable ATX 3.1 unit from a stronger product line. Around 850W is plenty; 1000W is generally unnecessary unless you have unusually power-hungry components or want a lot of headroom.