So I was wondering like is there some logic behind it all so it negotiates when the adapter is installed, or does it just add the supply to the power rails? Does a faster charging device need to negotiate to do so, or does it just need a certain supply on a 2 wire usb cable for example?
This is possible in theory, since whether the hub is bus-powered or self-powered is part of its configuration descriptor like any other USB device. However, once its negotiated with the host, this would require re-initializing and drop all the attached devices off the bus. I'm not sure if it's typical for hubs to do this or just always claim they are self powered even if the adapter isn't attached. It should be easy to check and compare the plugged/unplugged state in the descriptor information from
lsusb -v.
Strictly speaking, 'normal' USB only allows 100mA from the bus until negotiation with the host has completed with a request for more, then the maximum is up to 500mA depending on the power budget governed by the upstream network. To draw more within the standard as far as I know isn't really possible on a (USB1/2) host port. Dedicated charging ports are part of the spec, and allow 1.5A, so chargers can be detected by devices, but the detection takes over the data lines, so they can't also be host ports. USB-C ports can support USB-PD for a much more comprehensive negotiation of charging capabilities while also acting as full-fledged host ports, but obviously your old USB2 hub doesn't support this.
That said, many devices ignore the standards and draw more power than the spec allows, especially ones that only use USB for power and don't actually negotiate on the bus. Something USB spec compliant like a smartphone or tablet will only be able to draw 500mA from a USB2 host port.