Power has been fully restored at Sydney airport's domestic Terminal 2 after an outage lasting more than three hours on Friday morning - but for many passengers the wait is not over.

"Delays are expected to be ongoing because of the knock-on effects," a Sydney airport spokeswoman said.

Confusion and fatigue: passengers stranded at Sydney Airport. Credit:Patrick Begley

"It's affected some other airports; it ends up affecting the entire network."

The spokesperson said the source of the outage had been isolated to a substation but the cause remained unclear.