The definition of AZ on multiple places says "Unique physical locations within a region. Each zone is made up of one or more datacenters equipped with independent power, cooling, and networking".
Let’s take an example of an AZ with 3 DC’s. Are we saying that each of those 3 DC’s have independent power, cooling & networking or the AZ? If it’s on the AZ level then is it correct to assume that the 3 DC’s can be connected to the same power source?
From this page: https://azure.microsoft.com/en-ca/global-infrastructure/availability-zones/, official documentation says "Availability Zones are tolerant to data centre failures through redundancy and logical isolation of services." Therefore I believe that the DCs within an AZ are independent and will have separate power, network and other systems. The reason for this is to ensure that services are still available if one or more DCs go down.
Each Availability Zone is designed to be fault isolated from each other, so each AZ would have independent power. Multiple data centres within a single AZ may share power, but in practice, they would still be kept as separate as possible, as part of good engineering design.
So whilst a localized power outage may impact multiple data centres within an AZ, it may not necessarily affect the entire AZ.