Users often need to add or replace a hardware device and want to make sure (as much as reasonably possible) that it supports Ubuntu. Buying the device and trying it out may be impractical due to return policies or distances to a store in some areas. What are some good ways to know in advance if a device works with Ubuntu?
Note that this community-wiki question is designed to be the counterpart to Will my device work with Ubuntu?, which assumes that that you already have the device.
Questions regarding possible compatibility of a particular device should be closed as a duplicate of this question. However, questions regarding specific problems with a device should be handled individually.