How do live venues power on-stage monitors and sub-woofers?

Depends on the show. You'd be amazed at what you can run on a standard 13A wall socket over here - the fuses will pass 30A for a second, so you can get away with quite a bit.

If you want to go bigger than that, you're looking at Ceeform stuff. Pretty much every venue will have a 32A outlet you can use, and the bigger ones have something like a 125A 3-phase which will need a distro to get down to (for example) 12x 32A.

Chris
 
Talking about power... Usually there is one or more generator trucks behind the stage, or You have to contact the local electricity company for providing You with the amperage needed for the show. For example on the wedding farms were we perform Djing there is usually a 3*90 or 100 A Diesel generator, but it is also used for AC and the kitchen. That's why nowadays led's a are used for lighting. Unfortunately there aren't led ovens nor led AC's in order to lower amperage.