This is how volt nuttery starts
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Maybe it's the meter on your power supply that is off by the biggest margin.
After a while you have a stack of 8 1/2 digit DMM's and a bench full of LTZ1000 references and an automated measurement system that compares them to each other all year long.
I am just starting on this path. I thought about buying one of those voltage reference and resistance / capacitance test boards, Then thought a bit more about the cost of a decent one, and bought a BM869s instead. It still compares quite well against my other meters. A 30+ year old Dynatek 112, and a Wavetek Meterman 35XP.
I also bought 2 Aneng 8009 meters when they were all they hype, and I don't like them at all. They beep at you annoingly all the time and they are not reliable. I once bought a strip of 1k 1% resistors and wanted to test their tolerance, so I used my new AN8009, and I almost gave the aliexpress shop a negative review because the resistors were out of tolerance (by 2% or so), and this is a usual scam. Just to be sure, I verified it again with another meter, and the resistors were in spec. Then I fiddled a bit with the dial on the AN8009, and then it measured OK again. That was the last time I used those Aneng meters for anything. I had to wipe off a thick layer of dust to veryfy the type number of the aneng meters just now.
(The other 5 or so meters I have are not worth mentioning).
If you are serious / curious about calibration, then get some "decent" parts (10V voltage reference, some resistors, capacitors etc) and mount them on a board so they are easy to measure. And then once a year measure all the devices on that board with all your DMM's and log all the data. When one of your DMM's start deviating, there is something "wrong" with it. If all your DMM's suddenly start deviating, it is your reference board that is somehow wrong.
If you have higher quality meters, you can also have them calibrated every now and then, but this is to much to bother with and too costly for most DIY'ers.