So XT 600W vs. S12 II... S12 II wins? Is it more durable or something like that?
I don't know much about this,
The S12 has better components that are capable of running better than the XT when heat builds up. Heat will cause cheap parts to degrade and eventually fail. Cheap parts will also usually mean instability when the unit is being stressed.
I mean, you can take a chance with the XT. It might be totally fine, I would not though.
I have an old PC with a 750 Ultra LSP. It is not a high quality unit, but it has been running steadily for almost 7 years now. My XFXPRO 750W PSU (Seasonic built) runs fine too (3.5 years).
I actually bought a Corsair CXM 550W as a back up recently... just in case one of the PSUs fail.
@DaemonWarrior44 I should mention, MEC is right... the 520W S12-ii is cutting it pretty close. The 12v rail used to power the GPU and CPU will provide 480W total, not 520W. That is 40 amperes (amps) on that 12V rail. 40A x 12v = 480W