The main thing with these is that most Amiga's draw only a small amount on the -12V line. If you check the meanwell rt-50b datasheet there is a minimum current requirement of 0.1A (which is not too bad). On other meanwell models the minimum requirement can be higher, like 0.5A. Personally for 0.1A I add a power resistor across the -12V line to ensure it is drawing the minimum (e.g. 120R 2W or bigger like 5W to handle more heat). I've found this can stop the hum or whine you may get. I've never checked on a scope to see how much difference it makes.
But there are plenty of folks out there using them without fully loading the -12V line with no noticeable issues.
