Naturally, for a power amp, the first consideration is the power supply. There are two main types, the conventional, linear power supply, and the switched option.
This is the standard solution, and the least expensive. Most power amps used for small and medium rooms will have linear power supplies. The main consideration is the amount of heat they generate, as the performance of the amp can be compromised if there is too much heat radiating around the circuit boards.
Switched power supplies are more expensive, but they offer important advantages. Switching controls the level of heat generated and manages the quality of the power feed more efficiently. Switched power supplies are also substantially lighter than their linear cousins. For larger rigs, where several amps are being used, a switched supply is nigh-on essential.