Understanding Meanwell CV+CC driver characteristics
I have used the ELG 240 in the past, so I guess the same applies to the ELG-100.
If Vout is larger than 50% of max, so you will see a constant output, but there will be the usual ripple at the switching frequency ~100 kHz.
Even below 50% Vout, I was able to get a rather stable output. Down to well below 10 % Vout. However, the ripple frequency drops significantly. The output didnt go into DCM until very low Vout.