Step 4: Know what you looking for
I know that many older PCs often have capacitors on the motherboard, as most do most PCB's (printed circuit boards). Then it is simply locating the code for the 'size' of capacitors on the side of the component. ( if you need to learn more about components and how to identify them see my links in Step 1!).
Additionally I know that floppy and CDR drives usually contain small motors at the right voltage range; yeah I looked inside one that's how I know.