This whole thing is nuts
I admittedly don't fully understand the details, but the fact a state as prominent as Texas can get shut down like this from a winter storm that's probably "mild" to much of the country is unbelievable.
So in a very condensed nutshell, the three main players in texas power grid is ERCOT, private or public energy companies like reliant and txu energy, and then eletric utilities companies like Oncor. The way it works is that Energy companies actually create the electricity, utility companies like oncor manages the infrastructure to make sure that electricity gets to homes and businesses, and ERCOT makes sure that electricity is distributed in the most efficient way. Before the storm hit ERCOT assured everyone in Texas things would be fine, because all their models showed that even under peak load in this storm Texas would not even need the amount of power it averages for the summer, when just about the whole state is running their AC's 24 / 7. Problem is that is the summer, equipment doesn't get cold and freeze. Tree's don't get heavy with ice and snow and fall down. Gas lines don't freeze. So when the storm hit early Sunday night ERCOT told the energy providers "we need X amount of energy to keep everyone's lights on". When energy providers tried to deliver that amount of energy to the power grid, their were wide spread failures. Some plants shut down, some never even came online. Some had equipment failures due to the cold, snow, and ice and could only operate at a certain capacity. So energy providers were unable to give ERCOT the amount of energy they needed to insure they could get power to everyone in Texas. The only way to combat this until they can get additional capacity, aka the failed power stations back up and running, is rolling blackouts, where they move electricity from place to place for periods of time. The problem with this is that once they started rolling blackouts, there were still issues causing power to go out and they ACTUALLY LOST EVEN MORE POWER. These numbers are to keep things simple, but for example Denton is using 800 watts of power. But two cities near Denton, Corinth and Gainsville, have no power at all. So you decide to turn the power off for Denton for one hour, and move it to Gainsville for 1 hour, so people can heat their homes at least a little, because it is record low temps for Texas. That works. Then after an hour you shift the power to Corinth, so now it has power but Denton and Gainsville doesn't. But Corinth has some local issue with it's power, say the transformers stop working, and the power goes out. That 800 watss of power is COMPLETELY GONE NOW. Now instead of Corinth, Denton, and Gainsville having 800 watts of power rolling between them., or split between them, all 3 have NO POWER. Now imagine that happening dozens, if not 100's of times, over the state of Texas. Now you have to wait for a utility company like Oncor to come and fix the systems. But it is snowing, and sleeting, and roads are terrible, and its below 0 degrees in some places, so it is going to take a significant amount of time. And Oncor has to first discover where the problem even is. They might actually fix the local power issue in Corinth only to find out that their is also something wrong with the plant that Corinth is getting is power from. Pretty much electric whack a mole.
So the crux of the problem here is that the plants and equipment failed because they were not "winterized" meaning that no type of work was done to make sure the equipment was able to withstand the cold temperatures. For example in the winter, you might have an exposed water line outside that you need to wrap in insulation, to keep from freezing, that is "winterizing". And this is where we play the blame game. Texas legislators say they are not at fault because they have nothing to do with power supply, infrastructure, or management, so they point the finger at ERCOT. ERCOT says all we do is manage the power, and that was not the problem, the problem was not enough power, and that falls on energy companies who could not provide enough power. Energy companies say well the reason why we did not provide enough power is because the infrastructure could not hold up to the cold, and you never told us that we needed to design it or upgrade it to do so. Oncor is in the cut laughing saying "we not involved in this at all because we only do the maintenance work you asked of us and nobody asked us to "winterize" anything and that might not even be our job since we deal just about strictly with everything EXCEPT the actual power stations themselves."
In the end ERCOT is going to take the lion share of the blame, because they are the ones who were all up in the video days before the storm saying everything was going to fine.