Of course it should "be allowed" to increase tariffs. In my view, it's unjust and even immoral to use the power of the law to coerce or prevent what should otherwise be free commercial decisions.
But that's not all. In saying this, much else also needs to change.
For the very same reasons, all the laws that restrict, curtail, limit and forbid others from competing with Eskom must be scrapped forthwith. A state-entrenched monopoly or near-monopoly on any commercial activity - including the generation, distribution and resale of electricity - is in my view ipso facto unjust. It robs citizens of their basic and natural right to engage in uncoerced commerce, entrenches inefficiency and rent-seeking, and violates the basic precepts of a just and rational economic, legal, and political order.
So, yes. Eskom should not be prevented from doing as it pleases with its pricing. But neither should there be legal constraints on anyone else from generating their own electricity and reselling it to others in a free and open market.
The problem is Leviathan. We have too much State.
Of course, I know the chances of that changing are less than 0.01%. We're trapped in our own Statist thinking and self-inflicted powerlessness.