Could DE Sidious oneshot RotS Sidious with Force lightning?

By "oneshot" he has to win with a single stream of uncharged Force lightning within like 20 seconds.

I think so. RotS Sidious' lightning is capable of bending lightsabers. I don't think the younger Sheev can absorb it via Tutaminis or Lightsaber therefore he turns to ash.

No.

Definitely not.

Probably yes. Let’s see what @Azronger has to say.

Given how TFU Sidious handled Galen's suicide blast, it's definitely possible DE Sidious could one-shot RotS Sidious as the thread defines it.

I'd say yes.