It will not. P121 only has usb out ( type B socket) ( can only hook up to IPad or computer). Not external gear with USB or Midi unless you put a computer in between. $30 midi to usb converter will not work.

As we are aware, this will not work ( type A socket). Will not work even with type A to B adaptor because you need power.
https://www.amazon.com/TNP-Midi-Cable-In...w_1574228885856


that’s for KB Midi to computer USB and computer USB to KB midi.



To connect KB that only has USB out ( type B socket) to midi gear , you need the following.

You need USB ( host) to Midi DIn Connecter box which needs own power supply which defeats the portability purpose.



https://www.amazon.com/Kenton-Electronic...7880&sr=8-1

There are cheaper ones around $75, again , another box with adaptor.

Too bad, all sub $900 arrangers ( PSR 670, PA300. EK50) and sub $800 digital pianos no longer include MIDI connectors ( YAMAHA P125,P121, P45, Roland FP10,30). The only exception is Korg D1 and SP170 ( both sub $800 digital pianos ) and arranger wise, Roland BK 3 ( good job ! Roland to put both MIDI DIN and USB for sub $800 keyboard) and Korg microarranger ( $ 499 and now discontinued). The last sub $800 Yamaha portable digital pianos with MIDI outs were P35/95.


Manufacturers intentionally omit MIDI DIN in/ outs to make sure that you spend extra for MOTL and TOTL. ( Yamaha P515 and Roland FP 90 , both above $1000 have both USB and MIDI DiN connectors). Arranger wise, same is true for Korg PA 700 and Yamaha PSR S7xx or PSR SX 700 series.

I prefer simple single midi cable to connect to external gear without another box , adaptor and cables.