This is a good question to answer.
Generally, electricity value chain across the globe is the same, the only difference is the names of the players of the utility.
Nigeria unbundled its electrical utility on November 1, 2013, to investors (Investors are set of companies or individuals that spend money to maintain and buy utilities-water, electricity, etc)
Back to the value chain.
The value chain of Electricity is divided into four (4) major groups
1. The Power Generators
2. The Power Transmitters
3. The Power Distributors
4. The Power Consumers

1. Power Generators
These are the group of technical guys that generate power from different sources, be it Hydro, Gas, Coal, Nuclear, Biomass…
Specifically, we have 6 power generating companies in Nigeria. These companies generate power/electricity from hydro and gas-fired plants. The popular ones are Egbin Thermal Station in Ikorodu, Lagos (Gas fired), Kainji Dam in Niger (Hydro station), Shiroro, AFAM, Olorunsogo…
The major challenge these players faced is shortage of gas supply and/or debts accrued from buying gas on credit from oil companies like Shell and the likes.

2. The Power Transmitters
Basically called Transmission Company, they are the ones that wheel the power/electricity generated to substations to be picked by distribution companies.
In Nigeria, they are TCN- Transmission Company of Nigeria. The problem they are faced with is rigid cables, lack of transformers, poor network system…these are technical terms that would take forever to explain.

3. The Power Distributors (DisCos-Distribution Companies)
As the name implies, they distribute power they get supplied with from the transmission company. In our case, TCN is solely responsible for supplying electricity to the distribution companies that eventually power your house.
We have 11 Distribution companies in Nigeria
Abuja Electricity Distribution Company
Benin Electricity Distribution Company
Eko Electricity Distribution Company
Enugu Electricity Distribution Company
Ibadan Electricity Distribution Company
Ikeja Electricity Distribution Company
Jos Electricity Distribution Company
Kaduna Electricity Distribution Company
Kano Electricity Distribution Company
Port Harcourt Electricity Distribution Company
Yola Electricity Distribution Company
They all have areas of coverage within the federation.
All these DisCos are not responsible for generating light, they only distribute what they have been supplied.

4. The Power Consumers
This comprises of you and me.

What I want you to know is, do not ascribe blame to your distribution company whenever you do not have light.
A lot of things happens at the background which the general public does not know.