From manual...
9 V DC OUT jackWhen an AC adapter is used, you can connect a PCS-20A parallel DC cord (optional) to supply power to effects processors and other PSA adaptor-compatible gear.* Power cannot be supplied from the DC OUT jack when the NS-2 is running on batteries.* If you use the PCS-20A to supply power to devices that are compatible with PSA adaptors, make sure that the total current consumption of all devices (including the NS-2) does not exceed the maximum output current of the PSA series unit you’re using.
DC IN jackAccepts connection of an AC Adaptor (PSA series; sold separately). By using an AC Adaptor, you can play without being concerned about how much battery power you have left.* We recommend that you keep batteries installed in the unit even though you’ll be powering it with the AC adaptor. That way, you’ll be able to continue a performance even if the cord of the AC adaptor gets accidentally disconnected from the unit.* Use only the specified AC adaptor (PSA-series).* If the AC adaptor is connected while power is on, the power supply is drawn from the AC adaptor.
I use one out front with boost and overdrive in the pedal loop.