I'm sure the real smarty pants will have plenty of corrections for me, but when I was a young skinny person, I built a 70 volt DC supply and added a 68 ohm resistor, a switch, a 1k resistor, and an amp meter. I used alligator clips to connect each transistor up in the correct polarity at the collector and emitter with a 1k resistor from base to emitter. Turned on the 70 volts, and some of them shorted right there. Then I pressed the switch to allow 1 amp into the base, saw the meter show current flow, and let off the connection. If the transistor stopped, I called it good. Forty percent of the Mexican counterfiets failed. Then we built over a hundred multi- transistor power supplys. In the first year, 2 came back. One had a bad regulator chip and one had somebody stick a screwdriver in it and break the trim pot. The rest kept working and I never saw them again.