He did this right after he and I started talking about the problem at another forum. There was a radical drop that at times would be out of even the wide spec for voltage leveling listed in the manual for the APC-15 you use. Nice unit by the way and I have been looking at them closely for my own system.

EEman mentioned the inrush current a toroidal transformer can be capable of pulling. Now imagine there are eight or nine of them all trying to power up at the same time.