PSU light is flickering green. Otherwise no power Dell Inspiron 3847

Had a power outage the other day.  Once power was back, my Inspiron 3847 would no longer boot. No power at all. No light on power button. PSU had green light, but was dim and flickering / pulsing a bit.

I followed the PSU test from this page: ++https://www.dell.com/support/article/us/...

Steps tried:

• Opened up the case, and unplugged the PSU from all components. I plug in power, and light is full bright, solid green.
• When I plug in the 24 pin to the motherboard, it goes back to dim and flickering. (Motherboard was disconnected from everything else at the time)
• Swapped out the motherboard with another of same type. Light still dim and flickering.

The motherboard I swapped it with was a used one, and supposedly tested and working. So it's possible that one was also bad, but that doesn't seem likely, right?

Does this lead me back to a PSU issue?