I'm sure mine must also be SMPSUs - they are far too light (and probably too small) than to be otherwise. I haven't tested them to see how the output changes with varying loads (or no load) - so mine could be 'well regulated', but regulated to a different voltage from that written on the tinSounds like the could be uncontrolled, transformer supplies. The ones here, are all SMPSU's, and a quick check suggests they are tightly voltage regulated.
That was part of my thinking (probably rendering "+11%" not that big a deal). However, the main point of my last post was to indicate that if 4.5V is, indeed, the intended supply voltage (maybe already 'near the limit', as you say), then 5.6V (about +24%) doesn't seem to have done my LEDs any harm, over several years - as I said, it's the "PSUs" that seem to fail after a year or two, not the LEDs.Despite this, a couple of the chains have sections of LED's out, which was why I assumed they might be run near the limit. Unlike most LED's, they only need to survive a few days of Christmas.
Kind Regards, John