Both the Ancillary Shield booster capacitor booster modules require Cap Boosters.
What is displayed for both however, is the symbol for the loaded charge: a capacitor booster charge.
While this is consistent with how weapons and ammo are shown, weapons are all similar in function, whereas ancillary shield boosters and capacitor boosters have totally different functions.
If you fit a ship with both you can’t tell the difference between them on your display because both use the charge symbol instead of the module symbol. If you need to boost one, you can’t tell which one is which.
I seems more appropriate to show the “Shield Booster”, or “Capacitor symbol” symbol on your ship HUD so you can select the actual one you want without having to hover over it to see which is which.