I imagine you need a good strength base to "convert" to power
The Foundation of Power
Strength is the foundation on which Power is built.
Initially increasing Strength, increases Power.
Also, to increase Power, Strength needs to be increased.
The Caveat of Strength Training
There is some truth to, "Lifting heavy weight make you slow". If you only perform heavy Strength Training exercises, you Power and Speed will decrease.
Conjugate Training
A Training Program that implement Power and Strength Training elicits a greater increase in both; a synergistic effect occurs.
there are a couple of national judoka who do some sessions at my bjj gym just to brush up their newaza - they do a lot of power cleans or power clean+jerk.
Olympic Movements
The Olympic Training Exercises are Power Movements. Thus, they will increase Power.
For upper body work they do bench presses, pullups/chinups and rope climbs.
Upper Body
The Bench Press, Pullups/Chins and Rope Climbing are Strength Exercises.
However, some Power can be developed with the Bench Press by dropping the load down to around 48 to 62% of your 1 Repetition Max. Driving the weight up as hard and fast as you can, Compensatory Acceleration.
The same applies applies to developing some Power with Pullups/Chins via Band Assisted Pullups. Another alternative would be Lat Pulldowns or Rows with a moderate load, with the focus being on pulling as hard and fast as you can, Compensatory Acceleration.
Power Rules
Power Rules in Judo and most sports. Strength is important but to a lesser degree.
Kenny Croxdale