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Consider a hypothetical market where numerous producers sell identical candies.

The market forces of demand and supply determine the equilibrium, with Q1 candies sold at the market price of P1. The Buyers' benefit is represented by the consumer surplus, and the sellers' benefit is represented by the producer surplus.

Suppose the price of sugar, a key ingredient in candies, rises. This increases production costs and shifts the supply curve to the left. As a result, the equilibrium price rises, and the equilibrium quantity falls.

Consider the new consumer surplus and the initial consumer surplus. The new consumer surplus is smaller because of a higher equilibrium price and a lower equilibrium quantity.

Producer surplus experiences opposing effects. Consider the new producer surplus and the initial producer surplus. A portion of the initial producer surplus is lost. However, a portion of the initial consumer surplus is shifted to the new producer surplus. Consequently, the net change in producer surplus is ambiguous. 

In contrast, if there were an increase in supply, consumer surplus would rise, but the net change in producer surplus would remain ambiguous.