I have a radio controlled power switch (one that you plug in between the wall and a lamp to switch it on and off with a remote), that has an atmel microcontroller on it. I connected the radio switch to an atmel programmer (Gnd, Vcc(3.3v), Miso, Mosi, Clk, Rst). The atmel programmer is connected and powered via USB.
I accidentally left the programmer connected when I plugged in the radio switch and both the switch and the programmer blew up.
Now I wonder why.
The radio switch's power supply is a resistor followed by a 4 diodes (rectifier?) followed by a capacitor (filter?) followed by a VIPer12A switcher (provides lower voltage?).
I assume that somehow there was a voltage difference between Gnd of my USB port and Gnd of the radio switch, but how can that be?