So, Seems like the consensus is the GFI is bad. Which is exactly why I called out an electrician to replace it back in early November. When I emailed the customer to ask why he hadn't paid the bill yet he said he is still experiencing the same intermittent problem. The only reason I used the 10 y.o. transformer was that it was there already and I only added four fixtures, and it way under capacity to begin with. There is and has been a good in-use cover. I haven't actually been there since early November though, so I will swing by and see if he may have plugged Christmas lights in to the same outlet and propped the cover open. (I have seen that before.) Don't know where the breaker is. In a closet in the house I think. Probably more than 20 ft. away. I used the "amp clamp" of my Greenlee multimeter and didn't find a short. And as I mentioned to him, wouldn't the fuse have blown if there had been a short on the LV side?