alt Hacker News3.5" Floppies are either DD or HD. (there's more but let's keep it simple and practical)
A DD drive reads and writes DD floppies better than an HD one, but does not read/write HD floppies at all.
There's a hole in the floppy for write protection (hole covered = write enabled), and there's another hole on the opposite side to signal the floppy is HD. If it's missing, it is DD.
To recover a floppy, a USB drive is about the worst option, as they only expose a decoded floppy, and not the raw data, besides other annoyances.
You'll want a period correct HD FDD, or DD if your floppy is DD and your HD drive is having trouble with it, alongside GreaseWeazle[0].
As for that old 486, you'll want to open the case ASAP and remove the motherboard's CMOS battery, before it destroys the whole thing.
Capacitors aren't anywhere near a concern; most likely they're still fine, and will typically not destroy anything.