I used to use AC Outlet tester plugs in UK often - Very Useful and eady to use and understand, but have not been able to find any such items here. I now rely on a Multimeter and for my two PC I have a Toshino 4 and 5 plug surge protector power boards (bars). I do not plug my APC UPS in as the surge protection of the two may conflict with each other to some degree. The plug adapter bar also has two LED lights, one green one red which operate very similarly to the indicators on AC Outlet tester (only totally correct combination is Green on Red Off. (due to Ground not being Zero I am used to the Red glowing very slightly (cannot be seen in daylight or lighted room as on 3-6V normally). Both on means no ground. (I think Red on green off is reversed Live and Neutral connection.
Unfortunately my adapter's (the much newer one) Green LED light has failed but I can see the RED one and it that glows too brightly then I know negative to ground Volts have moved up from the usual 3-6V range. I suppose I should get a new one but it works fine and they are not particularly cheap (and
in my opinion although not low quality I believe not the highest quality either as I have found them rather fragile. I have yet to find a different or better make sold here.
To be honest there are a lot of very poor quality plugs, sockets and adapters etc. sold here. Many plug sockets (extension sockets using what looks and feels like thick tin, very easy to bend and poor at springing back into place when plugs are removed. As a result, plugs are often wobbly in their sockets after only a few inserts and removals. I insisted on all my house's grounded wall sockets being made by Panasonic coz I trusted that known Worldwide brand quality which was available locally). After nearly 10 years of use, it was a good decision as all sockets are still good and hold plugs tightly. Not saying there are not other quality brands here, but I knew of Panasonic and knew their products would be of acceptable good quality.
If you are interested Digerati take a quick look at
This is the Pathumthani (don't be worried about link which is OK, although it shows "This is the Pathumthani" which is just the person's new server name) and you will see what I try to avoid and some things that can easily fool the unwary or those with a basic understanding of electrical safety (and judging by the many recommended "so called" electricians who have come to quote or do small jobs I know a lot more than them (and often have more tools as well).
Regards