Hi!
Every time I shoot the enemy, it will create a random power up. It was some problems to pick it up when I stored the Game Object as a variable. I don't know why. But I tried one more time to use "Trigger Enter" on the power ups, and now it works. I don't know why it didn't work the first time. Maybe I did something wrong.
The object I have the action "Trigger Enter", needs to set to trigger and the object which enter the trigger, needs to have Rigid Body.
The problem is that, the object which enter the trigger, needs to move into the trigger. If it's not moving, the trigger doesn't work, if you know what I mean.