The adapters permit plugging in three-prong plugs without altering them. Unless the box is grounded, the pigtail (or screw hole) on the adapter is non-functional. Canada does not permit use of the adapters, so I am told. The permission in the USA stems from the fact that cutting off the third prong from a plug, as some users will do in desperation, destroys the grounding function until the plug is replaced. Better to use the adapter than to lose the ground on the cordset perhaps permanently.

Depending on how old the house is (after 1955) and, the house was wired properly, the outlet box itself is most likely grounded. You can use the adapter, just make sure the green wire that is attached to it is secured to the screw which holds the face plate on. That will provide a ground for whatever you plug into it.

You can't make an assumption based on the year of construction. I've seen 1958 houses without grounds, I've seen older ones with grounds. Even if there were a ground in the box, using that stupid clip/pigtail to the coverplate screw is a unreliable way of making the ground.

AT least for receptacles you plan on using for computers a d expensive electronics the best alternative is to run a new line with a ground.

You should also make sure the main panel has correct grounding electrodes also (a metal water pipe with at least ten feet in earth contact AND a driven rod ('made') electrode, or TWO driven rod electrodes).

Well this house is just full of surprises.

I took a look at the wiring in the GFCI in the upstairs bathroom. There is indeed a ground wire in that one at least, but things are still odd. If I plug in my tester, the lights show up weird with warnings. Also, the tripper doesn't turn off the receptacle when I try it on that tester.

Furthermore, it seems the power is being sent through the white wire instead of the black, despite being an end-of-the-run circuit. Does that make sense?

I thought something was up when I saw no electrical tape was wrapped around the screws, and the box looks a little beat up where I could see potential for a screw to touch the box.

I also noticed there was NO pigtail. I thought you always had to have a pigtail for ground? The person who installed this seems to have just did a half-loop around a box-screw, and then lopped the end of it to the receptacle green-screw. Is that allowed for end-of-the-run circuits?

I suggest you might want to have someone with some more expertise look at the wiring. Again, the fact that a plug in tester doesn't trip the GFCI probably means that there is no REAL ground connected (despite the presence of the wire).

What do you base your "power is fed via the white wire" determination?

There should be no reason to wrap screws with electrical tape in a proper installation.

As for the ground pigtail, the rule is that removing the receptacle should not interrupt the grounding. A pigtail is the usual way of doing this, but technically looping the ground wire around the screw fits the bill. It might not fly with some inspectors but the NEC doesn't preclude those type of through connections.

I put the probe on the white side (larger square prong), and put the other electrode to the ground, and then the light goes on indicating current.

Taxtax,

If you didn't disconnect the load, then all that you're doing is verifying that the white wire is part of the circuit. Disconnect the white wire from the load, and check it again.