Will a 520W PSU be enough for a Sapphire 9060 XT?

520W is above the 450W minimum, so yes, it should work. Your Ryzen 5600 isn't too demanding either, drawing just 65W. If you're really concerned about power consumption, you can lower the GPU's power limit a bit using AMD Adrenaline. But remember, it's best not to skimp on the PSU.

Your PSU should be fine; the 9060 XT isn't overly power-hungry. But just keep in mind that if you ever upgrade to something like a 9070 XT, you'll definitely want a 750W PSU to be safe.

That's a cool birthday gift! Your SeaSonic S12II 520W should technically work with the 9060 XT since it exceeds the recommended minimum. However, this PSU is getting old and may lack efficiency and protective features that newer ones have. With your Ryzen 5600 and the 9060 XT, you might hit around 480-500W total system draw at full load, which is pretty close to the limit. I'd suggest watching for any instability. If you can, upgrading to a 650W or 750W supply would give you better headroom for future upgrades. Also, are you considering any overclocking with this setup?

Yes, it should run, but your PSU is a rebranded RSY model which lacks over current protection. Getting a new PSU might be a wise choice. Montech has some affordable and reliable options if you're on a budget, so check those out!