Power utility Eskom on Wednesday called on consumers to switch off geysers, pool pumps and all non-e.
Activists had vowed to return to the streets yesterday, one day after mass arrests, teargas and water cannons broke up a protest by 1000 teachers and students in Manzini.
Maxwell Dlamini, president of the Swaziland National Union of Students, said a strong police presence had prevented people from gathering for the march.
"We have adopted a wait-and-see attitude," he said.
Two protest leaders were arrested in raids yesterday, with one kept under house arrest, according to Sipho Kunene, leader of the Swaziland Federation of Labour.
Police patrolled Manzini, arresting people in groups, including four teachers who were speaking to an AFP journalist in a cafe.
"We are not used to seeing so many soldiers. People are afraid of walking to town. I am afraid this is going to affect business," one Manzini resident said.
On Tuesday police used teargas and water cannon to disperse some 1000 teachers and students marching to the main city of Manzini, then stormed the teachers' union offices when the group sought refuge there.
At least 100 people were detained, including top labour and civil society leaders, according to union leaders.
The protesters want Mswati to loosen his grip on power and allow multi-party democracy, but are also angry at government proposals to slash salaries for civil servants amid a severe budget crisis.
Prime minister Barnabas Dlamini, a staunch royalist, has banned the protest, which began as a Facebook campaign modelled on uprisings in north Africa.
Police began setting up roadblocks late last week and have raided the homes of activists.
Most top union leaders who had been detained have now been released, according to Maxwell Dlamini, who was held from Sunday to Tuesday.
"We encourage people to stage protests wherever they are. It is difficult to get into Manzini or any city these days. We will see how we are adapting to the new situation," Maxwell Dlamini said.
The king has not spoken publicly about the protests, but sent his top advisers to meet with union leaders last week in a failed bid to convince them to drop the protest plan.