By the 2.5mm jack I meant a 2.5x5.5mm barrel connector, sorry for being unclear.
Yes, these are used for laptop power connectors at 4 Amps - and 7 Amps supposedly on the USFF machine on which I am typing but the fans are quite quiet and I doubt it is using anything near that - I will measure it later (by a power meter on the mains side). The connector is not warm, but anything beyond 4 Amps is quite an "ask" particularly of the spring connector in the "socket" (male part with the pin). Remember that power increases with the square of the current for any given resistance. You need serious cables for 18 A.
Also why would I need to feed power into the strip every 30 LEDs? I would like to have my strip still portable, I'd like to have it still roll up and be easily transportable with small setup
Well, you might like that, but the strip uses thin foil traces for the power with significant resistance. How well that would - at the end where you inject power - tolerate 18 A is very dubious to say the least though flat foil does radiate heat better than the same cross sectional area of round conductor.
The point is however that even if the foil does not fuse, there will be a substantial voltage drop along the length, so that when you attempt to display a lot of white, it will turn progressively yellow and orange as well as dim toward the end. This is because the blue LEDs require a higher voltage, so they will be the first to dim as the voltage drops, red the last.
You need to run a heavy cable with 5 V and of course, ground (because an electrical circuit always consists of two wires) along the strip and connect from this cable to the two power foils every 30 LEDs or so because there will be a 1.8 A potential draw at that point. Since the power will feed in both directions, perhaps every 60 LEDs will suffice.
I am also planning to get a 32x8 ws2812b panel which only has 3 inputs for power
Which three inputs? Presumably each end and halfway along. 15 A. So you need a feeder cable across the back connecting to each of those three. Because the panel is a lattice, the runs are shorter and the current distributed across multiple conductor traces.