There are a lot of options with transformers, and people have already mentioned a lot of choices. The nice part is you really aren't stuck with any option, you can always switch/upgrade. A lot of people have the transformer/power supply to run the trains, then use other transformers to power switches/lights/accessories. A lot depends on what layout you have at the time (and obviously if your layout grows, your needs can change. If you are running multiple trains at the same time, that draws more power. If you are only running a single train at a time, a Z-1000 would work for you, though if you also have a lot of accessories/switches, that would be underpowered).
One thing modern transformers (like the ZW-l, Z-4000) have in their favor is that they have built in circuit breakers that are fast blow. Older transformers as people have noted require fast blow breakers added on the outputs to the track (wouldn't hurt for auxiliary power like switches) since the breaker internally was designed to protect the transformer (Post war engines are built like bricks and are not sensitive to much; modern engines with circuit boards/components are somewhat fragile).
Almost every transformer could use a TVS (a kind of diode) across every track power (between the power/common output) to protect against power spikes (it is basically the same thing as power strips have for surges/spikes for electrical gear).
Again, this is by no means complete:
1)Lionel Post War transformers, like ZW/KW. These are the old standard bearers, they have fairly large outputs (the ZW is rated at like 275, but it is a lot less; KW was 190, again to track is a lot less). Advantage to these is they are rugged, they are pretty easily fixed since they are relatively simple, and you can get them fixed if you don't want to do it.
Another is they are affordable, unless it is some delusional person trying to fawn off a ZW as 'rare', you can get one that has been redone for around 100 bucks these days. ZW's if not used for track power, are really good for powering accessories and the like.
If you want to run conventional engines using a command control system (like legacy/tmcc), you can add a Powermaster between the transformer and the track, the powermaster will vary track voltage on command from the legacy/tmcc unit,allows remote control of conventional engines. Depending which variant you get (power output), they are like 100-140 bucks last I checked.
2)Lionel Modern transformers (CW, ZW variants except the new ZW-1). Advantage is they are modern, have good transformers, and are a lot cheaper than buying a new one. Disadvantage is they may not be easy to fix if they break, some of them also can have issues running conventional because the output is not true sine wave.
3)ZW-l. Lionel's current top end transformer. Has about as much power as you wish (well over 600 watts, have heard arguments about its real output). Looks like a postwar ZW but is entirely modern. Besides the power capability, it features the ability to control the variable output on all 4 channels via legacy/tmcc, so you don't have to buy powermasters (if you wanted variable control on all 4 channels, that would cost you at least 400 bucks if using powermasters). Has meters showing power status to the tracks, and to me is kind of cool looking. The downside is the price is really expensive, new they were well over 900 dollars, I saw a used one at York that was 800. The ZW-L from what I know doesn't produce "pure' sine wave, which can cause issues with performance with some post war engines (have heard people tell me they have never seen a problem, I have never had one, so I don't know).
4)MTH Z-4000. Modern transformer, has the built in protection, has plenty of power. Produces I believe pure sine wave, also has good circuit protection. They used to offer a remote that allowed using it to remotely control conventional engines (similar to the way the ZW-L does), but that hasn't been offered in a while. Z-4000's are just coming back into production (I don't know when the new ones will be available or if they are, the supply chain hurt MTH and the others a lot). As a result used ones are not cheap, and the new ones are well over 600.
To control conventional engines using this your best bet is get a MTH DCS setup, w TIU. The variable output on the TIU can control up to 2 engines plus of course allows command control of MTH PS 2 and 3 engines.
5)MRC transformers. They had (I don't know if they still make them) transformers for the 3 rail AC user. I have seen them used, and they are generally cheap. The downside on them (and again, just my impression) is from grumbling I have heard they don't work well with more than a few post war engines, and I think their largest output is much smaller than even the Lionel PW ZW.
The really important thing is deciding what kind of equipment you are going to run. If you are only going to run command control then you simply need a power supply that can provide 18v to the track or DCS TIU, and then have something that can run your accessories and the like. Almost any of the transformers as a power supply would work, or things like the power bricks that have been produced. Even if you want to run conventional, a DCS TIU can do variable output for conventional engines or a combination of a transformer with Lionel Powermasters and a legacy/TMCC control base can do the same thing.
In the end it comes down to budget and what you desire, there are tradeoffs with cost and how much work you need to do. Keep in mind the command control systems are not cheap (whenever they become available!), both of them are close to 600 bucks if not more these days on preorder, and thanks to scarcity legacy and DCS old generation systems are going for a fortune.
Again the nice part is any decision you make is not going to be wrong, all the choices can be made to work and if you upgrade it isn't hard to swap out a transformer. With command control systems currently not available (I don't know if Lionel started shipping the new base 3.0 yet, the legacy 'upgrade'), you could wire the layout for conventional block control and run it 'off the handles', then when those systems become available it isn't hard to add them to the system (really just a bit of rewiring).
Figure out what your wants and needs are, figure out the budget and that will likely guide you to what you need. If I had my desire, I would wire the layout using a ZW-L, get the new DCS and Base 3.0, use the DCS TIU for conventional remote control, and be done (I could save some money, buy the ZW-L and the base 3.0, for around 1400+, but still steep for me). However, at current prices that will be like 2k or more, so isn't in my budget, so I likely will wire for conventional control using my postwar ZW, and do it so adding DCS and Cab 3.0 later will be easy do do (for example, wiring the power to the track where there is only 1 power feeder per district/block), that can then be used for DCS signal as well as track power).
Others will have much more direct thoughts, these are just mine.
