D3100 and an old flash?

I have a Nikon D3100. Some days ago I found an old flash in the basement. It looks like a black brick, about 6, 5x5x3, 5 ( cm ), has a hot shoe stand but it is really only a bent piece of metal, so no syncing there. Out of the bottom go two cables - One goes into the power connector and the second one is a PC cable. In the front, there's written in red letters: FIL 4IM

So, I heard about these old flashes giving a nice voltage kick to the new cameras through the hot shoe, so I would like to know whether it is the same through a PC cable + PC fem to hot shoe adapter. I also heard that Nikons have higher tolerance to this back voltage than Canons.

So the question is: Would this flash be safe for my camera, when used with a PC-to-hotshoe adapter? Are there any other options?

Thanks.

Added (1). I don't know which one is more powerful, but I can't try off-camera flashing with the onboard flash - that's why I want to try this. Thanks for your answer

Added (2). FIL 4IM is the model name of the flash. But I found no info about it.

Added (3). Caoedhen: The dial is only for info, it does not do anything. There are no batteries, as I wrote, it goes right into 220V AC power plug. And the capacitor works perfectly, it flashes nicely and charges really fast

There's no way to know with out a brand and model number.

From your description, I would not attempt using it. It may well be that the on-board flash on your D3100 is more powerful than the one you found in the basement

It's Russian, I think… 1 found 1 link to a message board in Russia, with a small photo of a flash calculator dial. Just the dial. Google can't find anything else at all about the flash.

Wein Safe Sync with PC socket would work. Have you even looked into the flash power requirements? If this is as old as I think it is, it probably doesn't use AA batteries. It would use an old mercury battery that you can't find any more, and it will be an odd size. Do you have that battery? You could probably work around a replacement, IF you can find the output specs. And if the flash capacitor is not completely dead.

All in all, it would probably be easier, and cheaper in the end, to just buy a new flash.