PSA-120, , ACA-120: The difference between the PSA-120 and the ACA-120
The Boss PSA-120 is a regulated power supply, which means that regardless of
the load, it consistently provides 9 volts. The ACA-120's voltage drops as its load increases. Since each effect pedal may vary regarding its current draw and how voltage is used for the different internal components, it's always advised to use the recommended power supply. This information can be found in the specification section in the manual.