Eskom said it would escalate scheduled power cuts to "Stage 4" from 4 pm until midnight on Thursday due to a shortage of generation capacity.
The utility had earlier announced "Stage 2" power cuts during the evening peak hours for Wednesday and Thursday, which would have required up to 2,000 megawatts to be shed from the national grid.
Eskom said in a statement that there had been a delay in returning several generation units to service, while others had broken down.
It will also implement "Stage 2" power cuts on Thursday between 5 a.m. and 4 p.m., Eskom said, adding that it expects to repeat the same on Friday from 5 a.m. until midnight.
The struggling state-owned company suspended scheduled electricity outages 11 days ago, following several weeks of regular power cuts that prompted public anger and hampered businesses.
Eskom has an ageing power station fleet comprised mainly of coal plants that are highly prone to faults.
Government efforts to add additional capacity have been slow, and this year a record amount of electricity is set to be cut from the grid.