United Kingdom

The watchdog said that in previous winters some electricity generators had deliberately stopped generating power early in the afternoon, meaning plants were switched off during the crucial evening spike in demand. They would then offer to resume generating power later in the day, cashing in on the greatly increased prices on offer via the balancing mechanism.

Sounds rather similar to the behaviour of a little energy company based in the USA called Enron:

After the passage of the deregulation law, California had a total of 38 Stage 3 rolling blackouts declared, until federal regulators intervened in June 2001. [...] Subsequently, Enron traders were revealed as intentionally encouraging the removal of power from the market during California's energy crisis by encouraging suppliers to shut down plants to perform unnecessary maintenance, as documented in recordings made at the time. These acts contributed to the need for rolling blackouts, which adversely affected many businesses dependent upon a reliable supply of electricity, and inconvenienced a large number of retail customers. This scattered supply increased the price, and Enron traders were thus able to sell power at premium prices, sometimes up to a factor of 20 × its normal peak value. https://en.m.wikipedia.org/wiki/Enron