I know back in the day when they first came out I occasionally saw a strobe on top; I think one of the amusement bussiness related magazines had a circuit described, not sure if it was ever officially supported by Williams, nor was I ever able to find out the details, but I did come up with something that works.
Originally I though of putting one together from individual parts, or modifying an of-the-shell unit to trigger it internally, but I was not comfortable dealing with the high voltages present and potentially exposing the rest of the electronics to damage. I suppose if you went with an LED strobe, rather than xenon, the risk would be much lower and easier to connect.
I eventually kind of cheated, but it works quite well: I got one of the old classic style box strobe units, and directly switched 120v line voltage to it on and off using an SSR (Solid State Relay), the top device in the photo (the lower regular relay is for the GI flashing). I hooked the bulbs under the flash insert to trigger the SSR, and ran 120v through the switched side to an outlet that the strobe lamp plugs into. Even though the 120v pulse is very short, the strobe charges up and fires so fast that even a brief pulse is enough to flash it several times. Not sure if all strobe units will work, but the simple one I got does. The unit has a dial to adjust the flash rate, and you can easily set a point where it almost always flashes just once, although you can change it to flash several times if you want a different effect.
The SSR I used requires a 5v supply to activate, since I wanted to only drive this when the game was active, not strobe all the time during atract mode. I don't remember the exact details how I did this, but I think I hooked up to the flipper relay somehow so that only when the flippers are active during a game is the relay enabled. If you want to always have the strobe flash, even in atract mode, you can use a simpler SSR that does not require extra 5v power.
A bit of hack, but it works quiet well. Not sure if this approach will shorten the life expectancy of the strobe, but I have been using it for years without trouble. At some point I need to record a video of how this looks and possibly wired up, including how I got all the GI to flash as well...IMG_20200303_100333 (resized).jpgIMG_20200303_100348 (resized).jpgIMG_20200303_100303 (resized).jpg