Any experience adding a LPS to a stock Sutherland Duo phono stage?

And by the way, you would need two separate PSs or you would need to re-wire the unit to run. off a single PS that could supply both audio circuits.  That's a complex job.  Even to bypass the built in PSs with a pair of external PSs is not trivial.  And, as I said, you would be hard pressed to find an outboard aftermarket PS that surpasses what you already have.  The vast majority of aftermarket linear PSs are designed to outperform a wall wart or some other slightly more sophisticated design, not to compete with the linear PS of an expensive phono stage like that of the Duo.

Ron has reply to me that installing the LPS is feasible and could be done at Sutherland’s factory or by a technician upon receiving the boards. He has suggested me to stick with the current version considering the hassle tradeoff vs small improvement. 
ill go duos locos in the future. 

I assure you that the power supplies in your Duo are already "linear" type power supplies.  The term refers to a conventional method for deriving DC voltages and current to run the audio circuit. AC from the wall goes through a transformer to alter voltage and current as needed by the circuit. The voltage that appears on the PS transformer secondaries is rectified (converted to DC but still noisy, using solid state diodes, then filtered, using capacitors or a combination of inductors and capacitors to remove noise (any AC riding in the DC).  In a high end preamp like yours, the resulting DC voltages are in addition regulated.  Voltage regulation adds additional smoothing.  This has been done in audio for at least 80 years.  Only recently we have '''Switch mode" power supplies, or SMPS.  You find such SMPSs in less expensive gear but if done well, SMPSs can be very high quality. Nevertheless, audiophiles have been convinced to favor linear PSs in their higher end gear.

Thanks!