I guess the real lesson to be learned (regardless of the bit about
outdoor music and divine intervention g) is that, if you can't
supply _all_ the kit yourself, then you need to take along some basic
test kit to debug the other guys supply arrangements....

Yup. I set up some kit on a yacht, where the captain proudly presented
me with an extension lead he had wired from schuko plug to UK sockets
board. He had managed to connect live to neutral, neutral to earth and
earth to live. Those test plugs, very worthwhile.