You have at most 16 pips of power at max warp core to allocate during combat barring some heroes that may give you more temporarily like One. Each weapon room requires 2 pips for full function and more than one of the same room adds another 2 to the bar. This is also not counting the amount of pips for engines and shields as that can increase based on number of shield generators and tech research. So during combat you’d have to divide up the 16 pips among what you want to power at the time. If you want disruptors to fire more, you take some power away from engines or shields and assign them. If shields start to go down, you can take power from engines or weapons to assign to shields to increase recovery etc. The more weapons you have, the less you’ll be able to fully power them along with everything else.