In Apple ][, Apple ][+, Apple ///, Apple Macintosh 128k, Apple Macintosh 512k, Apple Macintosh Plus, and many old PCs such as IBM and Commodore PCs, have RIFA brand capacitors. They are used to filter out interference from power input. But they are unnecessary and the outer plastic casing cracks over time. This lets in moisture and rapidly explodes and causes violent clouds of white smoke that smells like a campfire with wet wood and leaves in it. So open up your power supplies and clip out
those caps immediately! They don't need to be replaced but you should replace them to be safe. Just remember to use caution working in power supplies, because there are high-voltage capacitors inside!
Image of an exploded RIFA cap:
