It appears to be a switching power supply. I suspect this because the white diode at the top of the picture looks like a high speed switching diode and it is mounted on long leads for heatsinking.
The diodes in question may be high speed types. That is, fast recovery diodes. Determine the voltage rating of the capacitor the diodes drive, multiply by three or four (or more), and chose a diode that is rated fast recovery, the voltage determined, and 1 to 3 amps. And, they may be Schottkey diodes, which are inherently very fast.
