Quite right!  The answer is nine 500-Watt PAR cans.  Remember that P=VI, so each socket will carry just 4.8kW as the supply voltage is 240V.

 

 

 

We are yet again with Dieter and the lighting rig.  Now they are in US and the janator at the venue tells Dieter that the sockets for lighting rigs are all rated 20 amps and are single phase.  His trusty multimeter now tells him that the mains voltage is 110V AC.   Now, how many PAR cans can Dieter run from each socket without blowing the fuses?