I am not privy to the exact figures but a simple google search provides me with the following data:
India:
As of October, we have an installed capacity of 1,82,689.62 MW (
Power Sector at a Glance ALL INDIA )
Population of India: 1.21 billion people (2011 census)
capacity per capita: 150.983 MW/million inhabitants.
Pakistan:
~ 20000 MW (
Daily Times - Leading News Resource of Pakistan )
Note: Please provide a better source if available. I was unable to find any in open source!
Population of Pakistan: 177 million (estimated -
Pakistan )
capacity per capita: 112.99 MW/ million
So based on installed capacity alone, we can see a major difference though the figures for pakistan are suspect at this point due to lack of any recent census data apart from the question of actual installed capacity.
Add to this the fact that most of Pakistan's installed capacity is based on expensive fuel oil based generation unlike India and I can easily see the logic of India supplying power to Pakistan!