"In an interview, the interviewer literally has all the power, and saying "no" or refusing to answer a question posed by the interviewer seems rather difficult."

If you feel like the interviewer has all the power in an interview, then it'll be difficult to negotiate your salary. You'll do things like give a concrete number when they ask you what your salary was at your last job.

The only time I would feel like an interviewer has all the power over me is if I was a new grad with no work experience.

An interview is a two-way street, you're trying to find out if you want to work for them as much as they're trying to find out if they want to hire you.