I'm using an Edimax EW-7811Un in my Raspberry Pi 2 under Raspbian. Version is
Linux stickpi 3.18.7-v7+ #755 SMP PREEMPT Thu Feb 12 17:20:48 GMT 2015 armv7l (or at least that's the closest I can find).
Every time even a single byte tries to go through the adapter, the Pi reboots itself. Including when the Pi is fetching the real-time clock on boot. Using
ifdown wlan0 and
ifup wlan0 to refresh the DHCP doesn't reboot, however.
The network I'm trying to connect to is configured with a password that I'm certain I've entered correctly, however it requires an additional log-on via a web browser for reasons that are most likely out of the scope of this question - the mere act of connecting to which also causes the reboot to occur.
An Ethernet connection is a no-go until ~4:30 PM Eastern, but I can ferry files via thumb drive if needed.
I wouldn't know if it's any value to diagnosis, but the adapter and the USB port both have gotten warm during my attempts to fix this myself. Switching to other ports don't help.