On Wednesday, December 19, 2018 at 9:22:10 AM UTC-5, wrote:

Only if the frequency is different, which I doubt as they are all the same model. What I need is a way of detecting if they're flashing together.

There are two possibilities.
1) The LEDS flicker at the line rate.
In this case they will probably all be in sync.


The LEDs flicker at the PSU switching rate.
In this case they will NOT be in sync. Switching power supplies are usually free running and the frequency will be drifting around. Even if they are the same model, component tolerances and temperature variations will mean they are on slightly different frequencies and there will be no defined phase relationship.

mark

+1

But I doubt the first mode is possible in a properly functioning switching
power supply. And AFAIK in a typical switching PS the latter never makes
it to the output and if it did, it would be so fast that you would not
be able to see it.