Fast rectifier diodes in parallel at SMPS
Beware of thermal runaway

When two diodes aren't exactly equal (which is the case with actual diodes you buy in a shop), the current through the branches will slightly vary. Due to  this difference in current, the diode with highest current will start warming up slightly, resulting in a slightly better conductivity. The current further increases with respect to the parallel diode and warms up even further. After a little while the current through one of the diodes may be substantially larger than the current through the other diode, possibly stressed beyond its specifications.

You can reduce this effect by using a tight thermal coupling between the diodes, but it is better practice to use either a diode that is spec'd for the total current or add a small series resistor to each of the diodes to improve currents shared equally amongst them.