I'm a landlord

Ah. As someone whose parents have been landlords for almost 40 years, allow me to speak your language then.

If there was a rain storm and a tree knocked down the powerline down the block and now the entire block--including your building--lost power, you would not be obligated to give your tenants free rent. If you don't charge your tennants utilities, you wouldn't be obligated to do anything for them at all, and if you do include utilities in the rent, then whether or not you owed them anything would likely depend on whether or not the power company gave you, as the person actually paying the electric bill, any kind of credit. Beyond that, it would entirely depend on the nature of the lease agreement. Additionally, it would not be your responsibility to fix the problem at hand, because the problem is not with your building or your property (as a matter of fact, because it's not on your property you wouldn't even be able to do anything, legally), it would be the responsibility of the electric company, and if the tree whose branch fell on the power line was on private property, the responsibility of that property owner to get their tree pruned.

And on the topic of the lease agreement, lets look at your attitude regarding the ToS through that frame of mind as well. If one of your tenants tried to break part of the lease or make demands not covered by their lease, or tried to renegotiate any kind of clause that you had included in your lease after the fact (say you have a guest clause, a clause regarding overuse of utilities or a liability/ exculpatory clause in the lease), and then tell you that when they signed the lease they "didn't agree to it then," you and I both know that whether or not they "agreed to it" is completely irrelevant in light of the fact that they did, in fact, sign the lease, which in the eyes of the law means that they did, in fact, agree to it.