Trinity's first and second abilities are actually amazing. There are two ways to use them (always together)
1. Use Well of Life, and immediately cast energy vampire on the same target
This makes it so the energy vampire target does not die. It effectively creates an energy battery with a surprinsingly good radius. Your teammates will also probably stop shooting it, noticing that it is levitated.
2. Use Well of Life, wait until 3/4's through the skill, and then use energy vampire
This is a huge nuke. Energy vampire does damage based on the maximum health of the target - well of life makes the targets health go up to a huge number (10x). When Well of Life wears off, Energy Vampire continues to tick for the max health number.
Energy Vampire is also very useful by itself. Pick a heavy unit, or a high damaing unit, or an extremely mobile unit, and vampire it for a huge stun that happens to give energy to all of your teammates. The first tick happens right away, so you always get at least your energy back.