How to eliminate this mess...

Well, one step at a time.

Where we live as people who restore pinballs is in the middle of the question "how far do I go?"

Addams are worth the time and money, but I'll tell anybody that Addams have problems you don't find on any other machine. They get worn out in ways you don't see on any other pinball. Thus any Addams restoration is going to be a legendary amount of work relative to most any other restoration you do.

How far do you go?

Personally, I would pull the playfield out of the box, pull everything out of the bottom of the game and clean the wood and paint the inside of the box first. I'd put the metal power input box in a metal polisher after removing the german sticker and get it shiny. I'd replace the MOV just because I was there. Fresh ground strap. Fresh power cord. This restoration is worth the extra work.

I was watching a shipbuilder who was instructing new apprentices, and they put some braces in, some of them long, some of them short. He made them cut every brace to exactly the same angle... not because it mattered, but because he (and they) were going to be spending a lot of time working in the boat environment, and if you surround yourself with things done RIGHT you are constantly reminded to do the right thing.

So... a clean bottom box with a fresh coat of paint sets the tone.

Power into the transformer is wired correctly! So cut out the splice to the brick power supply, and cut out the wires that the brick power supply had running to the CPU.

My friend James told me early in my career that the single thing you can do that gives the greatest appearance of professionalism is to keep it clean. So keep it clean. Wash the wires, get the dirt and dust off them. If it's ugly, replace it with something beautiful.

While you are looking at the power in to the game and the power box, I would run another outlet to 120v AFTER the power switch. (The soldering iron power plug currently on the power box in the bottom of the game doesn't cut off when you shut off the power switch.) I like to power mods with a separate power supply, and having an outlet that cuts power off when you shut off the pinball will be helpful. It looks like somebody has put a mod into the 12V coming off the power board. Best practice... don't strain the 30+year old power board 12v supply with mods.

Other than that, you have 30+ years of ham-fisted technicians doing really wrong things here. You are going to be revisiting every single thing that they have messed up.

One step at a time.

So... how to eliminate this mess:

Get a clean work environment.
Start at the wall plug and consider replacing every single thing you come in contact with.
You are going to be living in the middle of the question "How far do I go", so be thinking about this both on a small scale (should I replace the pins in this connector?) and a big scale (should I replace the playfield and rebuild the entire wiring harness from scratch?).
Work harder than you think you should.
Put more money into it than you should.

This rebuild is going to be one of your 'legendary' accomplishments, and you only do a limited number of projects this scale in your entire life.

Make it worth it.

I think the first thing I would do is make sure you have the proper voltages coming out of the transformer.

If not , then its time for a new or used transformer.

If you do , then I would remove the switching power supply. Put everything back to stock and see what I have got going on at that point.

Your transformer is probably fine, switching power supply is more than likely just to power the g.i.

Seen this plenty of times before. The switching power supply is tapped into the +5VR and +12VR. This is usually done to work around WPC "resets". I have even removed these hacks and the machine worked perfectly fine - no resets. I guess some people (operators) did this as "insurance".

Hehe, the simple stuff.

Remove the hacked in power supply. Just clip the Brown and Blue wires off at J114 on the power driver board for now.

Check that you have about 9.5 volts AC on J101 on the Power Driver Board right side on pins 1 and 2 across the Red Wires. (A little less is fine...) Replace the 5A 250V fuse at F113 (+5v fuse). (EDIT: oops, had the wrong pins here, 1 and 2 are correct...)

Your LED's have probably not come on yet, I doubt it was just a fuse. If your LED's did come on, check the test points TP2 and TP3 for +5v and +12V. Truth be told, I just check the voltages at J117. I know that plug should have +5 and +12.

Even when the LED's come on you probably won't have enough voltage here.

Fix the power driver board. This is probably going to be replacing BR2, and correcting every repair done by the 'technicians' before you.

Put the power board back in the game. You need only plug in J101 and J102, to check voltages on the test points. If you've got good clean power great! Otherwise keep fixing until you've got power where you need it.

Once you've got a known good power driver board supplying good power, I would rebuild the power plug at J114 on the Power board and J210 on the CPU with trifurcon pins. Make it look clean, then plug things back in.

If you are concerned about 'why... why... why... would anyone DO THIS!!!'...

Well, I'm 60 miles away from my shop, I have a brick style power supply in my truck and I don't have a Bridge Rectifier, it's Friday night at 10:00 PM, and I have three other bars calling me for service. I can hack in an alternate power supply and get them 'good enough' to have them stop calling me when they hit both flipper buttons and the game goes 'BONG' and resets. I can fix it tomorrow, and if tomorrow never comes, so much the better. Maybe I can sell the game to somebody and never have to fix it.

If there were only some gullible fool out there who would buy it..

Good question!

For both Capacitors and Diodes (Bridge Rectifiers are four diodes in one case) (not zenar diodes), going up in voltage just means that IF they got that voltage they wouldn't explode.

So substituting 400V for 200V is fine. For BR2, you will be supplying less than 10V, so a maximum 400V or 200V won't matter.

Capacitors... Let's use an example. C5 is a 25V 15,000uf capacitor. You could go up to 35V, or even 50V. The voltage rating here just means that if you get that much voltage, will the capacitor explode. A 35V or 50V version of C5 might be huge, and not want to fit on the board, but electrically it would work.

If you substituted a 10V 15,000uf capacitor at C5, it would explode! You need a good voltage margin that is higher than than any voltage you are supplying to it.

Basically for voltages on capacitors and diodes and bridge rectifiers (not zenar diodes), you can always go up in voltage.

Now, on capacitors, the 15,000uf is important, and unless you are someone who has some understanding of how the circuit works you should always have the same 'uf', in this case 15,000uf.