“Do I have to plug in my Mackie SRM450s into a special outlet to make sure they get enough power?”
Not likely. The SRM450 is designed to operate from a standard 120 volt AC outlet. During normal operation, it draws under 1 amp of current, however under maximum SPL conditions, where the amplifiers in the SRM450 are clipping, the 120V model can draw as much as 2.5 amps. You should be able to connect two of them to a typical 15 amp electrical outlet and still have plenty of power left for your mixer and most stage gear.