Power sharing on non-urban V2 sites happens in quarters. 36/72/108/144 kW. Previous to sometime in 2019 or 2020, V2 sites would give priority to the car that arrived first, with the second car getting the leftovers rounded up to the nearest 36. If you're curious about why 36, it's because the Superchargers are comprised of four groups of three 12 kW charging modules, each group has a module on each of the three phases. After sometime in 2019 or 2020, Tesla changed the way sharing works; power is immediately split in half to 72 kW for each car when a second car plugs into an A/B pair. When the first car dips below 36 kW, the second car gets an allocation of up to 108 kW. These are all nominal figures and can vary up or down depending on grid voltage and equipment condition.
V3 Superchargers handle power sharing completely differently and can save a considerable amount of time when a station is busy. V3s have 4 stalls per cabinet plus the cabinets can share power between themselves (up to 7 cabinets) on a common DC bus, plus solar and battery storage can be installed on that same DC bus to provide extra power when the transformer is maxed out (and/or charge the cars from renewables). This allows cars to part at any stall at the site and receive the maximum available power, compared to V2 which requires users to spread themselves out and avoid sharing A/B pairs.
AC (grid) input on each cabinet is only 350 kW and the utility transformer could range anywhere from 500 kVA (500 kW at 1:1 power factor) to 1,000 kVA for an 8 stall V3 site (leaving room for future expansion) depending on what the utility can support at any given location. With neither solar nor battery storage on an 8 stall site with 8 cars charging, a V3 site would be limited to about 87.5 kW per vehicle due to the AC input limitation of the charging cabinets.