We generalize a model, proposed by Alvarado, of the electric power market by including the effects of control and communication. To simulate realistic markets, our model issues control signals only at given times and those signals are delayed during transmission. These two effects transform Alvarado's continuous system into a hybrid system, with consequential effects. The stability analysis of the new system reveals two important properties. First, there is an upper limit on the market clearing time and the delay of the price signal beyond which the system becomes unstable. Second, there is a counter-intuitive relationship between the market clearing time and price signal delay: when the market clearing time is relatively long, delaying the price signal can improve the market's stability while reducing the communication delay can destabilize the market. This counter-intuitive effect shows that the full impact of information technology on power markets can be significant and difficult to anticipate. Therefore, as markets are designed and regulated, careful attention should be paid to the effects of information technology on the market's dynamic behavior.