There was a recent thread about old studio strobes not powered up for years. The takeaway from it was a combination of ramping up the supply voltage and brief power-on time, stepping up the voltage and the time progressively unitl the capacitors had 're-foemed'.
(there was a url link here which no longer exists)
Without the voltage ramp up (it takes a variac). I would flip on power for a minute and then turn it off, and let the unit set for a while (without bleeding off power!). The flip it on for two minutes, then off, and let the unit set for a while (without bleeding off power!), Then 4 minutes, then 8 minutes, etc.
One reply said:
To re-form a cap that's not yet failed, apply power for short periods, short enough that the pressure doesn't rise.
The process I use is as follows, done every day at noon for a week.
Power the unit up for one minute, then off and leave it off until the next day.
For the next six days, double the ON time each day, i.e. 2, 4, 8, 15, 30, and 60 minutes.
At the end of the week, the re-form will either be successful or the cap(s) must be replaced.
If at any time the fuse or circuit breaker blows, the cap(s) must be replaced.