I tested a PSU yesterday. All lights started, and 1 by 1 they faded. I thought the PSU was damaged, so I got the exact same style computer that was in known working condition to test the PSU just to see what lights came on to compare. It did the exact same thing.
Turns out, the original PSU I checked was dead, yet the 2nd one was not dead... however, both yielded the same lights.