From what I have discovered Electrify America has a two tier system one for lower kilowatts and one for higher kilowatts. But from what I gathered in my last charge they charge by the kilowatts when you first plug-in. So I was charged the higher rate, Because I started out at 182 kW which put me in a higher tier. And that charge remained throughout my entire charge.
However, the last time I charged at a Tesla station that charged by the minute, it put me in two separate tiers And charged me a certain amount for the lower tier and another amount from higher tier.
Just to be clear: We drivers want to be charged by the kWh because that's what we get in the end.
Charger owners largely are OK with that, because frankly they don't quite yet know how to make a business out of charging. But when you look at it as a business, their biggest costs are that expensive charging stall, which in many cases costs $200,000 to put in, though that's inflated because government grants pay for a lot of that in many cases.
Owners want happy customers, and they also don't want customers to be confused, so they, like customers, prefer simplicity of pricing.
Some states allow charging by the kWh. Some forbid it, and the charger starts billing by time. Sometimes to reduce the unfairness that customers see to billing by time they do tiers, to make billing by time a little closer to billing by kWh.
Curiously, in some places the rule that forbids charging by the kWh comes from regulations that say only electric utilities may bill by the kWh. However, in Canada, the rule is that if you want to bill by the kWh, you must have a government certified measurement device that assures the billing is accurate to a small margin. The accurate measurement isn't that hard, it's the government inspection and certification that's hard. Most of us drivers would not care if the bill were of by 1%. Gas stations have to have this, you've seen the seal on them for their inspections. Gas stations make a lot more money per hour than EV chargers.
For a station operator, their costs are the source electricity from their utility (or alternately, they may have put in solar panels and batteries and may mix them with the utility) but mostly time on that expensive station, and parking space that they own or lease (or sometimes get free.) A large part of the cost was just installing a megawatt power service from the grid and trenching etc.
So if a station were billing "cost plus" that cost would be a mix of the actual electricity bill and a portion of all those capital costs, plus financing over the life of the station. But that's too complex for customers to really understand, so they just come up with a price. If the charging is fast, they make it a high price, and when it's slow they make it a low price -- for the same result -- or they find something else to pay for it (like getting you to stay at their hotel.)
And it's all complicated by the government subsidies, or the VW dieselgate penalties, or by Tesla just wanting to sell cars by making their cars the best car to have if you road trip.