Wishaw General in North Lanarkshire experienced the power cut between 08:45 and 16:00.
It meant one emergency patient was redirected to Hairmyres Hospital. NHS Lanarkshire said IT systems were also affected.
The hospital was powered by back-up generators until mains power was restored.
NHS Lanarkshire chief executive Calum Campbell said: "In the interest of patient safety and as a precautionary measure, we took the decision to reschedule a small number of surgical procedures based on clinical priority.
"The power interruption impacted on our diagnostic and IT systems, which have now been fully restored.
"As a result, some outpatient clinics have been affected and one emergency patient was redirected to Hairmyres Hospital.
"This is in line with our business and emergency continuity plans which worked to good effect."
He added: "All patients affected by the interruption have been rescheduled and we would like to apologise for any inconvenience this will have caused."
A hospital was forced to reschedule operations after losing power for more than seven hours.