FWIW: The Baofeng UV-5R HT supplies 3.3V through 100(*) ohms on the tip of the 3.5mm connector, not 5V as documented above. Also, the PTT is pulled up thru 10K to 3.3V, and the MIC+ connection line also has a more complex (constant current source?) pullup to 3.3V. [This is nice, as the PTT line can directly connect to a Raspberry Pi GPIO pin!]
There's a (wrong in several places, but you can get the idea of the general functions) schematic at http://static2.rigreference.com/manuals/baofeng/baofeng-uv5r-circuit-diagram.pdf
(*) Correction! The schematic says it's a 100 ohm pullup, one radio measured 10K and the other measured 100K, so it's anyone's guess what a particular radio might have installed. I'm going to mark this pin as "Not Useful".
Further study shows a DC bias of about half the battery voltage across the speaker due to the external speaker being connected to only half of the bridged output amplifier, so you might want to use a DC blocking capacitor.