OMG that can't be good. Likely killed at least the transformer and maybe more unless by some stroke of like the main fuse blew before doing any major damage.

I could see that as a $1000+ mistake if it took out the transformer & some boards.

You maybe lucky in that the varisitor inside the power box shorted and blew the games main fuse. I would check this first.

There is a possibility that there's not as much damage as you fear. As the above post suggests, if the game is protected by a MOV or a more complex TVSS circuit(transient voltage surge suppressor) that might have intercepted the overvoltage before it reached the transformer primary (though those devices are mainly intended to guard against HV spikes from the powerline, and may actually be within normal operating parameters at 220v). Your first move should be to ensure that the transformer primary is receiving line voltage, and if it is not present then this may be the only fix needed.

Otherwise, the power supply is almost certainly borked, but the transformer may be OK (insulation is usually rated >=1kV in a typical step-down transformer's windings, so it likely did not develop any adjacent-turn shorting), and there is a reasonably good chance that the PS failed in a way that prevented any damaging overvoltage spikes from reaching the logic or driver circuits. Unfortunately, it is unlikely that any fuses saved the day as they are designed to blow with overcurrent conditions rather than overvoltage (and are typically rated at 250v), but they should be checked anyway.

Start by measuring voltages at the output of the power supplies. If they measure normally (unlikely), the downstream logic and/or driver boards may have sustained damage. If any are dead or out of spec, measure the PS input voltages (transformer secondaries) and if they are within normal limits then you have isolated the problem to the power supply board, and replacement or repair may fix the game.

I hate hearing thigs like this

I'm not optimistic that the damage will be low, but the transformer is likely going to be fine as the 8 amp main power fuse will have protected it, my guess is it blew as the primary would have seen essentially double the normal current draw. ( I=V/R ).

if he can test individual boards he should pull the MPU and see if it boots, if it does than he's probably in good shape. If he cant bench test this, he can always replace the main fuse turn it on and see what happens.

Once repaired he should change it to operate on 220V...this is actually really easy to do.

Maybe, I wouldn't count on it though as the same part is used in all machines, it's brakeover voltage is 275V.

Im confused how this could happen — thought 220v sockets would be impossible to plug 110 plugs into? Are they different in Brazil than in Europe? Been a while but could have sworn the 220s in Europe are round prong?

Wow, I didn't know about the Brazilian outlets..........
Brazilian outlets (resized).jpg
south-america-outlets-and-adapters-1637155south-america-outlets-and-adapters-1637155_final-5be0a957c9e77c005176ef38 (resized).pn

Oh wow that’s crazy!