Future Trunks uses this technique against Cell as part of his 3rd Grade Super Saiyan transformation. When he finds out he was just a little bit stronger than Vegeta, Future Trunks powers up and increased his power. Eventually, it is revealed that his muscles are so big that his speed is decreased, making him lose the match.
Appearances in games
Inexperienced Power Up is introduced as one of Super Trunks' Blast 1/Super Attacks in Dragon Ball Z: Budokai Tenkaichi 2 and Dragon Ball Z: Budokai Tenkaichi 3. Using this technique requires three blast stocks. It exponentially raises Future Trunks' attack power, but reduces his power up speed (similar to Pump Up). It also gives Future Trunks MAX Power.
Inexperienced Power Up reappears in Dragon Ball: Raging Blast, and Dragon Ball: Raging Blast 2 as one of Super Trunks' Super Attacks. Using this technique will increase Future Trunks' melee attack power, but his energy bar will drain in the meantime. When his energy bar is completely drained, the technique will end.
In Battle of Z, it is called Power Charge.