The TU-3 uses the BOSS PSA Series power adapter.
Note: The TU-3 draws 20 mA (DC 9 V) to 80 mA (DC 9 V, when High Brightness mode is on). Any PSA adaptor (200 mA/500 mA) is compatible. However, if you are supplying power to other effects pedals via the TU-3's DC OUT jack and the total current consumption of the TU-3 and connected pedals exceeds 200 mA, please use a PSA-S or PSA-S2 adaptor.
CAUTION: The use of any other power adapter may cause malfunction or permanent damage to the TU-3.