Eleven lighted passenger cars and four engines? They may not be over the 200 watts, but I'll bet they're getting close.
Another possibility is the old circuit breaker is failing or at least mis-adjusted. The way to really test this is to do a load test on the bench. What used to be a good load is old automotive headlight bulbs, they are in the 50-60 watt range. That transformer should be able to light three of them indefinitely at 12-14 volts output.
