Hmmm...
If you can work out how much current flows through the transformer then you can work out power i.e: P = I x V

Using my Gottlieb EMs I can only hazard a guess here but if the mains transformer has a 5 amp slo blow fuse then lets say it actually sucks an average 2.5 amps at 240 volts then power consumption would be 600 Watts.

Of course the current consumption would vary between the machine being in full flight and sitting idle.