> switch provider

Isn’t Eversource the only provider?

That's not how it works. The supply rate (cost of electricity that Eversource/UI buys) is a pass through cost. By regulation, power companies purchase electricity every 6 months from the power generating companies. That rate went up for a variety of reasons. The delivery side (the part they make money on) didn't change.

The cost of electricity went up following the global impacts of the Ukraine war and the northeast's reliance on natural gas, which was the primary export of Russia. Europe is dependent on Russian gas, and when they cut the supply the gas had to come from everywhere else. This limited supply and raised prices, and the capacity bottleneck in the northeast further exasperated the problem. The utilities have been warning this would happen for months. Eversource's CEO sent a public letter to Biden asking for help: https://www.utilitydive.com/news/eversource-ceo-seeks-emergency-order-by-biden-to-ensure-gas-supplies-as-new/635356/