Quick answer
Cash is only useful after the grid can accept the power you make: confirm income, power capacity, and city upgrade state before buying the next source.
Decide whether to wait for cash, upgrade a city, expand power capacity, or buy the next Power a City generator.
If cash is slow, first check whether the city or power cap is blocking progress. The reviewed walkthrough shows a player hitting a maximum-power message, upgrading the city, then waiting or buying a Small Dam when cash and power were short.
The generation cash using observations note avoids a cash per second selling formula and any creator specific amount claimed.
cashgeneratorscity upgradepower gridvillages