Here’s what boss has to say about this pedal:

The BOSS TU-3 is the world’s go-to stompbox tuner, trusted by players everywhere for its reliable operation and bulletproof durability. Scaled down in size, the TU-3S gives you the same industry-standard performance in a tiny footprint that saves precious pedalboard space. The display and tuning functions are identical to the TU-3—the only thing eliminated is the pedal switch. Always on and ready to go, the TU-3S is perfect for use with pedal switching systems like the BOSS ES-8 and ES-5, and ideal for any setup where space is at a premium

This pedal is used, has been tested and is fully funcitonal. Does not come with power supply.