In 9 out of 10 cases it's the power supply.
The typical cheap chinese mb102 power supply is "specified" for 6.5 V to 12 V.
I won't run it at 12V. Easy to check with finger if it's getting hot.
30V? No.
Wiring is important to check especially on a breadboard.
Burning wires with 250 mA: no
Solid wire needed? No
Additional cap: can help
Do you have better flash success using lower baud rates?
Then maybe the usb adapter or its cable maybe a problem, too.
Cal