Would it make sense and be safe to put power conditioner in front of PS Audio regenerator?

"I could also experiment more with power cords from the wall but this Purist works well,"

Unnecessary audionervosa.

I use a PPP. It's 18 years old. PS Audio refreshed it in 2020, and good for another  10 years. They no longer support it.

The output display ISN'T 100% accurate depending on the calibration of the output/ display. There's  an adjustment pot underneath  the unit to fine tune it, which is done at the factory to display 120V.

With a Google  search and  a MM it can be done, if you're  a tinkerer. If you don't have experience with live circuit boards, best to just leave it be.

"Do you think that newer PS Audio P5 would be significantly better ?"

P5 is 2 generations old. Long discontinued. A newer PP isn't  going to magically transform  your system. If anything the psychological  "new box" will be in play for a hot minute. Naturally, just my take on using a PP.

"I wonder if audiophile grade outlet would help."

Listening to your setup from 11:00PM to 4:00 AM while the grid is less strained will probably yield better results than buying more audiophool accessories.