We always use the power provided by the contest. Our FE's are older and it could just be the boards in those units are more stable. I have nothing to which they can be compared. Although I cannot directly answer your question, I have an alternate solution you could consider. . . .
How about buying a couple of deep cycle batteries, a good sized inverter, and a battery charger. I'm not great with electronics, so someone else would have to tell you how to get these all hooked up to work together (I'm mostly talking about getting the two batteries wired together so they will both work with the system I'm about to describe). Set it all up so that you plug your FE into the inverter. Obviously the inverter is drawing power from the two batteries. Then the charger is hooked to the batteries and you draw contest power to continually charge those batteries. The results are two fold. One, you get the stable power you need to run your pit while constantly charging your batteries. Two, if the event would lose power, you have no worries, because those two batteries will run your pit for 24 - 30 hours, no problem. With this set up, you would never have to worry about whether an event has good power or not. Just a thought . . .
I like Merl's answer to call and talk to Stuart. I think he'll actually refer you to Tony, but give it a shot . . .
Rod