The USB to PSL 30N PCB is a board that can power up to 8 Seimitsu PSL-30N buttons.
By using the 5V contained in the USB connections, you can easily power your Seimitsu PSL-30-N buttons.
The card has a line of terminals for ground and a second line for +5V.
This card to be used in passthru of a USB controller card allows to recover the +5V/GND.