If it’s OK with your power supply, congratulation, you’re lucky! Keep using it. Some power supply has slightly higher voltage even if it’s labeled as 9V.
My Gator power supply has 9.4v output from “9v out” but I felt it’s not enough because it sounded too lo-fi and max delay time was too long compared to with included power supply.
I guess Memory Boy doesn’t have a function to regulate the power voltage, which other analog delays have. Anyway, it’s very sensitve to power voltage. Someone says delay time varys day by day, or club by club.

Or, simply, EH improved later issues.

I found delay time seems to be dependent on power voltage.

Lower the voltage, longer the delay time and make stretched-tape-echo-like lo-fi sound. It will go far beyond 550ms and, at max, delay sound can stop. Higer the voltage, clearer the sound and shorter the delay time.

According to my measurement, at least 9.5v is needed for “proper” work.
So if you use standard power supply which has around 9v, it won’t work correctly.
I can get 9.78v with included power supply even from 100v outlet in Japan but it’s inconvenient not to be able to use standard 9v power supply.
It’s EH’s fault, I think. At least, “work with 9v power supply” isn’t true.

I made regulator circuit with LM317 IC by my self and got 9.7v from 18v output of my Gator power supply with no problem, but EH should improve this kind of instability.