I have one of those over fancy battery chargers made for the RC market. It uses a MOSFET load to directly measure the current and voltage into the variable set load to find the battery capacity. It's kinda small so it can only do 25W or so discharge rates max, but any lower discharge rate is available (via transwarp drive, and if you are doing 25W discharge on a 3.7V battery it may get really hot, the battery not the charger). It can also run multiple charge/discharge cycles automatically to find a battery 'average' capacity at any charging rate and discharging rate you program. I was tired of new battery types needing a upgrade to my charger a few years ago.
I bet that two high current resistors on a USB stick beats what I paid for it by a long shot though. I love the translation in the description of the part above...
It's normal when welding resistance may occur heated white smoke or odor phenomenon.
Don't worry that is just your usb port catching on fire.