It might work well enough without burning anything up, etc., if you get the phasing right, etc., which isn't hard to do. The problem is you do not know until you try it.
It's not the way I would do it though and I don't expect it would be as satisfactory as having one large supply with the proper size feed wires to places spaced around the loop.
However, I doubt you would hurt anything by trying it, so why not? It might work. It might not. But it's most likely to almost work - work but with a few noticeable pannoyances.
The reaosn is that there are two issues at work on the "feed a big loop" issue and you might solve only one and not the other: the two reasons you might need more than one "Wall Wart" are:
-capacity - one wart might not be enough for multiple trains (you mentioned more than one but did not say how many). Wall warts eachrun one train well but if you had three or four trains with lighted cars you might need three or four of these small power supplies just to provide enough power.
- voltage drop. The reason feed wires are run to different places spaced around a loop is that voltage drop can be an issue. Track conducts power, yes, but not always well enough around a long loop with lots of connections between track sections. You can see and hear (in chuff rate, etc.) a two-volt difference drop in a 16-volt (at the power supply) feed as a loco goes around a loop: it will speed up and slowdown noticeably. Running adequately-sized feed wire to various points on the loop to keep voltage within about 1 volt of a constant value is common practice to avoid this.
The right way to power a big loop where multiple trains will run is to take a large supply, say a 180 watt brick, and connect it via multiple feed wires. You now know you have 180 W of power - enough to run three or four trains - maybe more. And if you size the feed wires correctly, for ten amps (maximum output of the brick), then you know you won't have bad voltage drop anywhere. Problems solved: you know you have both the capacity and the voltage constancy you need.
If you do it the way you propose, using multiple wall warts connected to points on the loop using their factory supplied feed wires, all you know is that you can run one train near each feed location. For example, say the wall warts are 32 watts each (I'm not sure what they are, 1.8A at 18V? Let's say that is it for the sake of argument). Six would give you more than 180W capacity (190W actually): so you could run six small (less than 32 W) trains if they all spaced themselves out so they always run with one and only one nearest each power outlet. But you don't know what will happen if two or more bunch up, or three, other than if voltage drop is an issue where on the loop, the nearest power supply isn't powerful enough to run all three, and that even two might cause such a dip in voltage in their location that they would slow down - then others would catch up with them, making the problem worse - and . . . annoyance!
My guess is that for running two or three trains, with six spaced out around, say a 100 foot Fastrack loop, six times 32W would give you only about the equivalent of 100W capacity: probably run 3 trains satsifactorily but maybe not four.
