Variac power on current surge
Power surges or big inrush current is definitely associated with transformers be they auto or regular. It happens when they are switched on at the zero crossing of the voltage cycle. Yes, I said the zero crossing point. This produces the biggest peak in flux density and if the core saturates too much then the circuit trips.

Convince yourself, by communicating with the supplier, that inrush current is not a problem. By the way, starting a transformer on full load slightly reduces the inrush current problem. It's not prima facea gut-feeling logic but it's true