Add a Linear power supply or iFi SPDIF Purifier2?

I am currently using a Naim Unitiserve streaming from a Western Digital NAS, then using coaxial to a APL DSD-S DAC.  I am considering to spend several hundred dollars to add some tweaks rather than spending $2000+ to buy a new streamer/server.  I am considering replacing the switch mode power supply with a linear power supply, or the iFi SPDIF Purifier2.  
 

For the LPS, since I am not planning to spend a lot of money, I am going to try one of those from China which the quality is a bit of an unknown.  But I think it should still be better than the original power supply.  

For the I Purifier2, I read it reclock the signal going into the DAC.  However, the APL convert the signal to DSD first.  I am guess that conversion should do some clean up or reclocking, so I am not sure if the iPurifier will be beneficial.

Which one do you think will offer a bigger improvement?