mains vs power source

mains

noun
  • The domestic electrical power supply. 

  • The pipes of a centralized water supply that transport the water to individual buildings. 

  • The farm attached to a mansion house. 

  • The main course of a meal. 

power source

noun
  • A source of power such as a generator or mains outlet. 

How often have the words mains and power source occurred in a corpus of books? (source: Google Ngram Viewer )