My old converter had a toroidal core transformer. Looks like a donut with wire wrapped around and down through the center. Anyway it was getting hot, every now and then I'd smell something but couldn't find the problem. It finally got hot enough to burn away some of the enamel coating on the wire and short the transformer.
I don't think there was ever a intermittent power problem just the final melt down. I did a lot of searching and found that my unit wasn't known for it's longevity. I swapped my 55 amp out for a PD9260 that done a fantastic job keeping the batteries charged without boiling away the water.