Just goes to show - don't always blame the A-B kit, which IMHO has an unparalleled name for stability and reliability if the installation is sound.
Another point is that the SLC power supplies are the very least sensitive to mains-borne transients and drop-outs that I have ever seen in industrial power supplies. I'm gonna be lazy and not look the specs up - but they are very tolerant of "brown-outs".