Shouldn’t Do This, but…

@noromance I texted the landlord with that NEC citation and that didn’t go over very well. He said, ‘no one goes into the basement without me, why do you need to get into the breaker box’? At which point I made up some nonsense. I’m not living in a gentrified part of the city. There are six houses on my street and everything else around me are industrial complexes. Anyway, I’m looking at the Goal Zero 500X lithium generator and that would make the in the wall receptacle a moot point.  But speaking of the landlord, he’s regular people and when it comes to my stereo, regular people see me as eccentric.

Just tell him you need to upgrade the outlet for some sensitive electronics and you'll pay for it. If he pushes back, tell him if it didn't matter you wouldn't be asking.

And, the NEC 240 24.b is the real deal. If he won't comply, call it in to the city. It's like gravity, it not just a good idea, it's the law. 

NEC 240 . 24 (B) says each occupant shall have ready access to all overcurrent devices supplying the occupancy 

Sounds like there might be a lot of non compliant work down there.  Are you sure the building is a legal dwelling unit?  Check with your local government.

When i owned a 2 flat my renters always had access to to breaker box in case I wasn't around to reset it for them. By right's you should have access to the electrical box in case something trips, or happens so you are able to reset the breaker.. Ask him what happens if he is not around if the a/c should trip the breaker will he always be around to reset it, plus @panzrwagn is correct it is the law to have access, unless he dosen't have it up to code and dosen't want to show it to you..I am reaching here but.... contacting the city inspector to verify your rights

is not a bad idea hope this helps