"Delivery manager" is basically how people say "project manager" now. Their job is to set priorities, triage incoming issues, make sure everyone knows what everyone else is doing (when relevant); coordinate with third parties or external integrations, etc. Product owner is who you're building the product for - in client services it would be your client; for internal projects it would be who is "driving" (more bizspeak) the project - could be the CEO or a marketing person or a VP or whatever. Tech Lead is responsible for making technical decisions, architecture, hopefully writing some code, etc.
"Project Manager" has negative stigma. I'm not entirely sure why, but I think the perception has to do with the way that project management might be done in larger organizations - concern for minutia and TPS reports over actual accomplishments.
The Project Management Institute and their certification process has led to a situation where project management is seen as a domain-agnostic discipline. As a result, many certified project managers know little about the domains they are managing. Furthermore, coming from the construction industry, many of the traditional project management processes and thought is linear and waterfall in nature. They have taken steps to adopt agile and iterative processes in the past few years, but bear great legacy costs when it comes to applying project management to technology projects (where many projects fail for a variety of reasons).
