The sf-500p12a seems good - LLC resonant + DC-DC. The other model gives me mixed answers, some sites spec it having APFC, DC-DC, Multiple 12V rails, whereas others don't.
The is also a difference between the sf-500p12a modular and non modular version.
Could you please link where you're buying from? That would give us a better idea of the PSUs in question, and there may be other options.
500w is already more than enough, even for a 1080ti upgrade. What is more important is quality.