Problems persist on Adelaide trains

South Australia's Transport Minister Stephen Mullighan says he shares the frustration and anger of train passengers after a power failure brought some Adelaide services to a standstill.

But Mr Mullighan says he can't say for sure when the southern suburbs rail network will return to normal, with some delays possible over the weekend for fans flocking to Adelaide Oval for the AFL match on Saturday and the A-League grand final on Sunday.

"The government cannot apologise enough, I certainly apologise to all those commuters who have been inconvenienced," Mr Mullighan told reporters on Friday.

"I completely understand people's frustration and their anger when the services that they expect to use aren't being provided reliably.

"Particularly when people are being held up for hours at a time. Particularly when people are stuck on trains in between train stations."

The Seaford and Tonsley lines, which carry about 15,000 passengers each day, went out early on Thursday morning, stranding peak-hour commuters.

The problem was tracked to a circuit breaker at a substation which tripped but engineers are yet to determine what caused it to fail, preventing the use of a back-up power supply.

Mr Mullighan said good progress was being made but he couldn't be certain when the problem would be fixed, the system tested and services returned to normal.

Diesel rail cars and substitute buses, offering free rides, were used for a second day on Friday and would continue to be deployed for the afternoon peak-hour.