This EX-800 is fully functional and in good condition. It does not include a power supply. (9V DC Negative Tip)
The EX-800 is the desktop version of the Poly-800 synthesizer, an 8 voice analog polyphonic synthesizer with 1 DCO per voice 24dB Low Pass VCF, 3 Envelope Generators, patch memory, & MIDI I/O.
This one has been modified with a knob for cutoff frequency, resonance, and filter FM. With these you have direct access to the listed parameters and can fine tune the sound more easily.