There is actually a whole political thing developing around this between renewable energy opponents and proponents. Ostensibly, the blackout was caused by a main transmission line (interstate feeder) being knocked over, disrupting frequency synchronisation, and activating failsafes.

However, because SA gets 40% of its energy from wind farms, it's now being suggested that having more local baseload capacity in the form of fossil fuels may have prevented this.

Ironically, the severity of the storm itself (it's being a called the worst storm in 50 years) is being blamed on climate change.

I guess we'll see what's true and what's not in due course.