Apparent PSU problem

I have an older extra PC (ASUS H97M Plus motherboard - i3-4150 CPU - 12GB Kingston
HyperX DDR3-1600 RAM) that I use for Windows 10 Insider Preview beta builds. It has
a PS/2 keyboard that I've been using to start the system (CTRL+ESC). That start
method stopped working a couple of weeks ago and I had to resort to the start button.
That started failing and now won't start at all. I connected the power supply to a
tester that showed all power levels OK, but the PG indicator was dim and blinking off
occasionally. That was sufficient to cause me to order another PSU (Thermaltake TR2
430W since I'm using onboard graphics and don't have to power a GPU). The old one in
the system is an Antec TRU 430 that has to be at least 14 or 15 years old. Is there
anything else I should have checked before deciding the PSU was the culprit? Other
than the recent start problems, everything else has been working well as usual.

Larc