The power failure, which began Sunday night, left Delhi, Punjab, Haryana, Uttar Pradesh, Himachal Pradesh and Rajasthan states, along with the capital without power for more than 15 hours, the Press Trust of India reported.
The outage affected at least 300 trains in the region, Indian railway spokesman Anil Kumar Saxena told CNN.
More than 350 million people live in the region.
"When the northern grid failed, we started taking power from eastern and western grids," Indian Power Minister Sushilkumar Shinde said.
The blackout stranded passengers at train stations, and signal failures created traffic tie-ups in Delhi's already congested roads, CNN reported.
The cause was not immediately known but official sources told The Times of India excessive usage might be to blame.
Shinde, who ordered an investigation into the outage, said the last time an entire grid failed in north India was a decade ago.