After Buffy ended there was a scifi cartoon series called Futurama that had an episode parodying "Once More, With Feeling".
The Robot Devil made the cast inexplicably burst into song and sing random things they wouldn't otherwise say.
In the series all their robots are built in Mexico, and no date was given for when that factory came online, just that the "Friendly Robot Company" was started by persons unknown a very long time ago.
The Robotico Diablo (robot devil) line in Angel could have been a nod to Futurama's parody of Buffy by doing a little shout out to them.