You could be right it could be scaled to ship size rather than reactor power. Either way +100 reactor power is a drop in the bucket on a Battleship
My preference with Aux Slots is to start each class with one Aux Slot (put with the Core Components, rather than hull sections) and then increase through techs, while making nearly all Aux Slot utilities either percentile bonuses or scaled to hull size. Costs would either also scale to hull size or not (only if the thing they improve doesn't itself scale to hull size, like perhaps a sensor effect improvement). I would also look at costs for FTL Drives to be scaled to hull size, as these move larger hulls, versus Sensors or Computers.
For Reactor Boosters in particular, it's odd that they improve by 100% (Tier-1 tech) and then another 100% (basically T3) over the base unit (T0). It would make more more sense if the techs were at T2 and T4, compound 50% increases (like weapons are compound 30%) for effect, and just be x2/x3 for base cost (since they're basically insignificant). So T0 Reactor Booster is +20% Power for 5/10/20/40, T2 Improved RB is +30% for 10/20/40/80, and T4 Advanced RB is +45% for 15/30/60/120.
For the max usage situation above, with these changes applied, the Jump Drive goes up from -30 Power to -240 Power, the Shield Capacitor goes from -20 to -160, and the Adv Afterburner goes from -20 to -160, but the Adv RB is +900 per on a Zero-Point Reactor. So with just one Aux Slot for an Adv RB, you'd be 55 power short (or just 15 short if you went with Neutron Launchers instead of Matter Disintegrators) on the most extreme Power usage. More likely at least one of the Psionic Shields would be armor or hull plating and make it easy to reach.
It's still a bit overpowered (bah-dumb-bum-TSSH!), as I'd prefer more of a sacrifice to get the ultimate power-hungry build. Compound +30% increases over 20% base would be just 26% and 34% - certainly more sacrificial, as just dropping one Psionic Shield isn't enough to offset the shortfall- while +40% increases would be 28% and 39/40%, and still reachable with just one armor or hull plating. Changing the base bonus is probably better for making the sacrifice more meaningful, with 15% base being compounded to 300/400/520 at 30%, 300/420/600 at 40%, and 300/460/700 at 50% (Adv RB still only takes dropping two Psionic Shields or swapping out the Enigmatic Decoder for a 2nd Adv RB), or with 10% base being compounded to 200/260/340 at 30%, 200/280/400 at 40%, and 200/300/460 at 50% (one Adv RB only works with just three Psionic Shields at any increase rate, two Adv RB (plus dropping the Decoder) are still short by two Shields at 30% and by one at 40/50%).
