Your mistakes on stage are your own fault. You are a performer. Good performers don’t blame their tools. If your laptop flakes out, or your movie won’t play, you are responsible. If you have special needs, let the organizers know early and ask for a rehearsal. If you can’t get one, simplify. If at the rehearsal the tech guy is on drugs, or the organizer seems overwhelmed, simplify. It’s your show and you will be judged regardless of where you point fingers. Practice and prepare accordingly. Have a simple 5/10 minute fallback version of your talk you can do even if the there’s no electricity.