I measured the leaks between the leak source and a big metal surface. So for correctly measure the darger of a leaking I'll need to measure between the leak source and neutral or ground.

...and you have to measure the current, not voltage. And anything below 1mA is considered safe current. But of course, it should match what is to be expected with that device, so there is only the intended current path, not any extra unintended one (e.g. from some isolation fault which may deteriorate over time into some higher, above safe limit current).

So e.g. with a SMPS adapter you may expect 1..5nF of Y capacitors, so currents of about 72..360uA are normal.
A touch sensor dimmer would have 2..10MOhm separation resistors between the touch surface and the phase input electronic, so currents of about 20..120uA are to be expected as normal, the voltage probes use to use 1MOhm resistor in series with about 70V glow bottle, so about 180uA are normal. Vs a small adapter using just a small 50Hz transformer exhibitting leakage of 50uA is not normal, because there is supposed to be no designed leakage (the transformer may have about 10pF, so no more than 1uA), so such transformer is likely faulty.