It's hard to find the right AC adapter for the Twin, but I understand that 9V is ok to use. But is 1A enough amperage? The system requires 1.25A, but some say that 1A is ok.
If the console tells you to use 1.25A then these rules must always be respected and I will encourage to use an AC adapter at least 1.25A only, those commonly available like 1.5A should be good, as well as 2A. I will never use 1A AC adapter unless you ONLY want to test it for a while to check if it works, otherwise never plug it into the console