Tesla have two different types of charger (soon to be 3) and there is a ‘nack’ to getting the best out of them. The short version is they share power so spread out across the site.
The long version is:
V2 superchargers and they can be identified easily, they have 2 plugs on very short cables (CCS and Tesla only type 2). They are labeled 1A, 1B, 2a, 2B etc.
These are 140kw 400V dual bay chargers meaning the power is shared between A and B. If there is a car plugged into A and B, the most you’ll get is about 70kw, single car will get the full 140kw. These are pretty long in the tooth these days.
V3 superchargers have a single CCS plug. There are 2 stall designs one similar to the V2 but has one CCS plug on a short cable. The other is newer universal design with a long cable and a card payment terminal built into it.
These are up to 250kw 400V but the power cabinet is usually only rated for up to 400kw and services 4 bays labeled A-D. The power cabinets can share power and shunt it so any stall in theory but it’s not always implemented or working so as a general rule, spread out across the site.
If the site is full, you’ll get ~100kw because of the overall power limit for the site. That’s not abnormal for most providers.
If you have an 800V car, you’ll not get decent speeds off these and is limited by the cars internal conversion to 800v process.
The soon to be released V4 supercharger (non in the U.K. yet) will be 500kw 800V. The ‘fun’ part is they will re-use the universal stall design from V3. A single power cabinet will now serve up to 8 stalls so the only way to tell it’s the new 800V one by looking is they will be labeled A-H or it might saw 500kw on it somewhere.