The session was extended by an hour into the evening after the outage, caused by a substation failure, plunged garages into darkness with engineers using torches as mechanics connected back-up generators.
"I came to the pits and said 'it's dark out here. I need to change my visor'. Then I realised there are no floodlights around," Mercedes' George Russell told Sky Sports television.
"It would have been hectic if this was an hour later and the sun had already set."
Seven-times world champion Lewis Hamilton had already done 70 laps, more than a full race distance, as he started official testing for Ferrari after his move from Mercedes at the end of last year.
The 40-year-old Briton, chasing a record eighth title in 2025, was fifth fastest in a morning session led by his Mercedes replacement, 18-year-old Italian Andrea Kimi Antonelli.
"Our focus right now is on experimenting with different things, gathering as much data as possible and getting familiar with the car, and we’ve already learned a lot," said Hamilton.
"It’s too early to really understand performance, but everything feels good."
Leclerc took over the car after lunch and was fourth overall.
Norris, last year's runner-up to Red Bull's four times world champion Max Verstappen and now the bookmakers' favourite, said it was nice to be back in the car after setting a day's best time of one minute 30.430 seconds.
"It was a good, fun day on track, and we progressed through a lot of the tests that we wanted to do. I’m looking forward to pushing the car a bit more over the next couple of days," he said.
New Zealander Liam Lawson, four-time world champion Max Verstappen's new Red Bull teammate, spun his new RB21 but was second fastest and 0.132 slower, with Williams' Alex Albon third.
Lawson did 58 laps and Albon 63 on a day that started breezy and chilly at around 14 degrees celsius.
Racing Bulls' Yuki Tsunoda, fourth on the timesheets, matched Antonelli's 78 lap tally, with British rookie Oliver Bearman completing 72 for Haas.
Australian rookie Jack Doohan was testing for Alpine, and ended the session sixth with 68 laps and compatriot Oscar Piastri was eighth for champions McLaren and did 66 laps.
Teams have three days of testing in Bahrain before the 24-race season starts in Australia on March 16.