if you are losing 80% or more fat you wont lose power, if you are losing muscle you may lose a little power but gain better condition and endurance.
Power for a boxer is mostly technique, i could throw a punch 50% harder in the ring but i choose not to telegaph or lose balance or jump into it.

What is yourtime scale for losing the weight, it could be too much too soon, always box at a weight you are comfatable with if you go to low you will be dehydrated and that will effect your preformance