I can't claim to be an expert on fun fairs. I only know about Dreamland because, back in the 1970s, I had to compile a list of non-standard electricity supplies in the South East and they were the last taking DC. They used DC motors in their rides for the smooth speed control they gave.
I imagine that the same consideration applies to mobile fun fair rides as well and, if they are generating their own electricity, there is no reason why it should not be DC. They don't need to worry about transmitting it. OTOH, these days, as DC motors are widely used in CNC machines, heavy duty DC motor controllers that accept AC input are much more common than they were 40 years ago.
Colin Bignell