Hi, there really is no way to tell when a power supply is going to pop right? I have a lot of vintage PC's and most of them still have the original power supply in them. I have had one pop on an IBM 5150 and an NEC 286. Luckily the 5150 still worked with a new supply after that but I trashed the 286. And is it better to leave these old computers on all day, or turn them off 3-5 times a day? I hear that it really puts a lot of stress on the system when it's turned on. I don't want to risk damaging anymore computers. And I think it's harder on an old 10MB full-height HDD than a new one! Any input appreciated!

Maybe you missed the responses to your earlier post Why don't they make computers that will do what we think we want them to do?

If they have been running this long, it's probably safe to rule out component failure due to manufacturing defects. The one problem which you will probably find is thermal stress related dry joints. Therefore leaving them running would be safer. Vintage PSUs had a problem with self destructing when sufficient load was not present. So a dry joint could destroy the PSU when it interupts supply to the 12V line. If you want to retain these relics of the computer era, I would recommend resoldering every joint at least every two years. Keep in mind that you cannot buy new replacements for these systems. You can only be given old ones. I understand that NASA has found dificulties like this!