There are a few things you need to pay attention to when you're looking for a powered mixer. Here's a quick run-down.
The Difference Between Standard Analogue Mixers and Powered Mixers
Unlike analogue mixers, powered mixers are equipped with an amplifier which means they can not only be used to mix microphone, instrument and line source signals, but also to directly plug in a pair of passive speakers. This way, you don't have to depend on an external amplifier.
The Pros and Cons of Powered Mixers
The biggest advantage of a mixer with a built-in amplifier is that it does away with the need for a standalone amplifier, which spares you from having to lug a hefty external amp around. Also, passive speakers are generally more affordable than active speakers. While a traditional analogue mixing desk is usually cheaper and more user-friendly than a powered mixer, the 'downside' of going for an analogue mixer means you'll either have to grab a pair of active speakers or pick up an external amplifier along with a set of passive speakers.
How Much Power Should The Built-In Amplifier Have?
We recommend opting for a powered mixer that has a built-in amplifier that's able to deliver more power than the RMS power capacity of your passive speakers. This way, you're ensuring there's enough headroom for the volume to be turned up without forcing the amplifier to its limits, which is something that could lead to distorted sound and may ultimately damage your gear beyond repair. For passive full-range speakers, we recommend an amplifier that packs at least 150% of the RMS power capacity of the speakers. For passive subwoofers, that would be 200%.