The Transwarp Computer doesn't boost your Power to 23, it boost the skill Warp Core Efficiency with 23.

Here is the Formula (From STOwiki.org)

**"The formula for the subsystem power bonus according to this post is:**

Subsystem Power Bonus = ( Skill Level / 300 ) * ( 75 - Current Subsystem Power Setting )

Example: A skill level of 100 and a current subsystem power setting of 25 will produce an efficiency bonus of +25"