This came in handy for me a few weeks ago. I don't work in the city anymore, so I'm never in a parking garage. But a few weeks ago I had occasion to be in town, at a garage with no dedicated EV charging.
I needed to get something for the ridiculous $14 the parking garage was going to charge me for all day, so I planned ahead. I took my Tesla supplied charge connector with me, with my 5-15 and 5-20 adapters.
Once in the garage, I began driving slowly and looking around. Really looking. Most garages don't have EV charging, but they still have lights. And on some of the roof support posts, they have 5-15 or 5-20 power outlets!
So I tried to find a spot on an upper level, where fewer cars would be parked or driving by my car. Fewer eyes to see and fewer people to ask questions. Then once on an upper level, I tried to park off in the back. Again, less eyes and opportunities for questions.
Then I was able to plug into a 5-20 and get 6 mph charging (it was only giving 108 volts) for the whole time I was in town. Not a lot, but something for my parking ticket fee!
And it wouldn't be a bad idea to put a piece of tape over the blinking green lights on the Tesla charge connector. Attracts less attention that way. If I were working in town regularly and parking at the same place all the time, I'd check in with the garage manager, but for one-off occasional use this can work.
I'll have to make this into a video for people to see online!