Sorry to nitpick, but you can't make that assumption. The MacBook uses USB-C Power Delivery. It simply will request which wattages are supported, and ramp up its usage to the limit of the attached charger. Devices between the charger and the MacBook can certainly limit the wattage.
Just because it charges, does not mean it charges for the full 87 watt. You can check this by connecting any charger, going to Apple menu -> About this Mac -> System Report. Then in System Report, check the left side. There's a Power item. When you select that, you can see at the bottom how much it's able to pull.