Another electricity market of similar scale that is also an energy-only market is the Australian NEM. It hasn't had an event similar to the ERCOT disaster of last winter yet, but there have been discussions about adding a capacity market mechanism.
1: There are multiple price caps that set a maximum price on energy. 2: There's a commonly traded instrument that effectively acts as an insurance product for retailers against high prices. This means peaking generators get paid every quarter, even if they plants don't run at all. 3: The Australian government is spending billions building pumped hydro and gas generators to ensure supply over and above what the private sector is willing to fund.
Do participants in ERCOT's system not trade energy swap contracts? Why?
None of that new pumped hydro is online yet though - existing pumped hydro capacity in the NEM is minor (essentially only Tumut and Wivenhoe).
One reason that the NEM has been fairly robust might be that it is divided into regions with only moderate-capacity interconnects, such that each region is managed to be able to "stand on its own".
I'd imagine our relatively milder climate also has a lot to do with it.
(The NEM has a wholesale spot price ceiling of AU$15,000/MWh, US$10,732 at current exchange rates or US$10,245 in PPP terms).
This measure does get triggered occasionally, generally after transmission or generation failures combined with hot weather.
But states have interconnections that make it more resilient.