depends on the Rega equipment you have -
PS1 350mA Power Supply will work for all Rega accessories and units except: Planar 1, 2, and 3, or Fono Mini A2D.
PS2 100mA Power Supply works with the current model Planar 1, 2, and 3 as well as the Fono Mini A2D.
What TT do you have and which model Fono ( there have been several versions ) do you have ?