Something in the analog board died. I doubt it was the powersupply since nothing changed when you replaced it. Probably needs to be recapped. I notice that once in a long while my SE will do that jittery screen thing. Usually only for a few seconds. Sometimes it would happen when I insert a floppy. But I've only seen it do it a few times. I've heard this means the analog board needs new caps. Mine probably will be fine for awhile as it rarely shows screen jitters. But it is showing it's age (as there is screen burn in enough that I can see a faint shadow of the menu bar. It's not bad enough to where I could see the original desktop icons. Just the faint outline of the desktop. But it does indicate that the screen/analog board has seen a lot of on time).

I'll probably wait until after I get my SE/30 before I can afford to recap the analog board in the SE.

As for your issue. Definitely sounds like bad caps in the analog board. It was probably limping along due to the old powersupply being a bit on the weak side. Once you replaced the power supply, it probably accelerated the death of the analog board.

You should probably send that analog board off to someone here who can replace caps. I've heard uniserver is the go to guy for this.