I'm using all magnetics and some are at least 40 years old. The capacitors in them are totally unlike the ones that failed in electronic devices so there is no relevance there. If the capacitor dies the bulb won't fire at all and and for $30 or so can be easily replaced. Try fixing a digital ballast.
They do not lose power output as they age and are much less susceptible to damage from voltage fluctuations compared to digital ballasts.
I still use a 16 year old 400W Hortilux conversion bulb in a 40 year old HPS ballast and the plants grow fine. A buddy recently sent me a 400W Philips CMH bulb and that's the one I'll be using for my veg bulb now and just keep the old Hort for a backup.
No noise from it, (have 2 like this one and an MH like it), need the extra heat for my cool grow room and never once had a bulb blow in almost 20 years.
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