Supporting SMT electrolytic capacitors in high vibration environments
RTV silicone is used for this (and to adhere components to PCBs permanently in general). The neutral cure kind that doesn't produce acetic acid and smell like vinegar when it cures. So not most of the stuff you will find in hardware stores.

RTV-162 is one of the purpose-designed silicones for this but it's almost more than double the cost of some other neutral cure alternatives like RTV-108 or RTV-6708. From comparing the datasheets, the main difference appears to be that RTV-162 is twice the hardness and strength.