We had a venue power failure during a large evangelical event - the pastor simply went to the lectern & commanded '20 minutes of silent prayer'...

Something like this happened on an awards ceremony I was runnjng in London. The power went out-lights, sound, AV the lot. Our presenter happened to be Roy Castle, who picked up his trumpet - brought onstage as a prop, and started to play the last post! Brought the house down until power was restored! Only answer to the original question - move in, engage and use the lungs you were given, but project don’t shout!

Engage directly with the audience. Make it interactive so that everyone can contribute. Maybe organise some games, interactive sessions.

After a little heart attack and a 60 seconds breathing exercise... I'll remember myself that I was once able to sing (a capella) "All by myself" like Céline Dion on Saturday nights with my friends when I was young. So I'll be able do it again. Even if Céline Dion is not involved. But just in case... I'll check with the sound team if we can work on a miracle together to save the night. (And the Queen.)

Engage with your audience. You can make this interactive by playing a game and getting the crowd involved. I once supported someone who always carried 2-3 Starbucks gift cards and to lighten the mood he would ask 3 from the audience to share a funny story. Most times he would hand out to the funniest story but other times he would give them all out.