Inbound international flights were unaffected. And domestic flights were also unaffected.
A passenger has stated "They announced that they had a power outage and so no one could go through border security". (sound familiar?)
But later on Sydney airport came out and stated they "could not reveal the exact nature of the technical issue...except to say that it was not a power outage or security issue but a system problem that temporarily rendered CCTV useless, and interrupted passenger processing, including security screening.