There's a list of accepted types of primary and secondary photo IDs at https://travel.state.gov/content/travel/en/passports/requirements/identification.html. One of the options there, listed under "Primary Photo IDs", is an "In-state, fully valid non-driver ID with photo".
But, when I tried to apply for a passport using my in-state, fully valid non-driver ID with photo as my "Primary Photo ID", the acceptance agent told me that a non-driver ID wasn't acceptable by itself; she claimed it would only count as a "Secondary Photo ID", and that I'd need to bring in e.g. a driver's license if I want to avoid using "Secondary Photo IDs" (which also requires that I have an "Identifying Witness" present with me, who has their own valid "Primary Photo ID", and I'm not sure that I know anyone who has a driver's license (NYC) that I can also convince to burn several hours at the post office.)
I tried asking the support email, NPIC@state.gov, about this; they replied with a list of primary photo IDs that contradicts what's shown on the travel.state.gov site and does not include "in-state, fully valid non-driver ID with photo". When I pointed out the contradiction, the support agent avoided my question about whether the Department of State website has incorrect information.
So, either the travel.state.gov website is wrong (!!!), and I need to get a driver's license in addition to my non-driver ID for the sole purpose of applying for a passport, or the two workers I've spoken with so far are wrong, and I need to figure out how to find an acceptance agent who understands the requirements correctly. How can I get an authoritative answer on this?