I finally had enough of not being able to charge at work today. I said the hell with it, I'm gonna try my 5-20 in that outlet!
I brought my charge adapter to work with me and mid morning, with few people in the building, I plugged it up for 5 minutes to get some numbers.
With the charge cable just plugged in, before the amps begin to ramp up, I have 121 volts. At 16 amps draw, it drops to 114 volts. If I dial the amps down to 8 or 10, the voltage floats around 117 to 118. I didn't get any power quality warnings.
114 volts at 16 amps was getting me 6 mph of charging.
Dammit manager, let me charge here!!!!! I think I'm due for a performance review, I'll offer charging instead of a pay raise, which I'm sure would be tiny anyway.
Yes, by my estimation a 5-20 gives you about 42% faster charge rate than the included 5-15 (you'd think it would be only 33% faster, but you have to take into account the overhead of running the computers, fans and cooling which is the same regardless of how you charge). So if you have a plug with that horizontal blade (see here for a picture CarCharging.us), then getting the 5-20 adapter is well worth your while.