Well I said I'd been wrong before. 11.5 volts on video card.
I finally got ticked off with the clumpiness of the video. Slow to paint, and even with pre-viewed photos in memory, they painted on the screen a segment at a time.
I measured the voltages on the dedicated supply to the card. 5v solid. and 11.5v with minute fluctuations. Viewing Good photography showed no dipping of voltage on either line.
I still thought Bow-lox to the notion that a 250 w PSU was the culprit, because the computer seemed stable in all other respects. I had to know.
I took an old AT PSU out of the junk box and compared ground voltages with the computer. I got 50v or so AC between them, but when I dropped the meter setting, (AVO8) it showed scarcely any more needle deflection. A good sign that the stray v was of very high impedance. I nailed the chassis together with a wire that could cope with 50 amps at least. Checked the voltages at all points as common.
Took a deep breath, and fired it up.
The effect was astonishing. The whole system had seemed to take on a new vibrancy, sluggish painting of the raster, now in a blink of the eye. I can still hardly believe it.
Disturbed a duff connection? We'll see when it's normalized again, but I don't think so.
I know that some of the dips would be of very short duration, an not show on a meter, but I had thought there would be a general lowering during heavy video processing. If there was, it was in milli-second bursts.
11.5v steady, just too low?
That's the only other notion. Time will tell.