I’ve been advised by my dealer not to plug in the turntable power supply because step down power supplies (24V output for TT motor) do not have stable power transformer and has no ground.
Has anyone else had issues with plugging TT power supply into a P3?
I have a P15, and I have always connected TT power supplies to it. Did your issues go away after removing the TT power?
Edit: Power supplies plugged into P15 were the TTPSU and the Neo for RP8 as well as the power supply of the Planar 10.
I have a vague recollection of once having seen warning information about plugging certain types of synchronous motors (like the one with my Scout) into AC regenerators. I don’t recall if it was in the Scout’s manual, or in the manual I had with my old PSA P500. At any rate, as a result I’ve always erred on the side of caution, and didn’t plug it into the P500 when I had it, and don’t plug it into my P3 now.
Edit: it was from the P500 manual, and it was only a warning not to use Multiwave: “Any turntable or equipment with AC synchronous motors, such as some cooling fans should not be used with MultiWave II. This equipment must be used with 60Hz SineWave mode.”
I never use Multiwave. I like its sound on Sine. However if the advice is to connect TT to mains directly, I could do just that 
I only had the P3 for a week. Day 1, it had a fault and caused the TT power supply to blow a fuse. Hence the advice not to plug it into the P3. Later in the week it, had two more faults which resulted in need replacement tube in my integrated amplifier.
Currently P3 back with dealer. Obviously a little nervous about using a P3 again.
If it is damaging gear, then it should definitely be checked.
Edit: Tube gear performs better with high regulation as opposed to low distortion. I am not familiar with P3, but believe it could be set as such.
@Serhan can you explain the difference between high regulation vs low distortion? Is this comparing regeneration vs filtering?
As far as I know, when you go the High Regulation vs Low Distortion (THD) settings and select High Regulation (default) it ensures the output voltage is delivered as precisely as possible, but at the expense of slightly higher THD. Selecting Low distortion mode would output the lowest possible distortion but with the potential of more fluctuations in the output voltage. I have always used High Regulation because my incoming distortion is anything between 0.4% and 0.8%, but my voltage moves between 223V and 238V depending on time and day. To the best of my knowledge, it is all regenerated power but with the option to direct the unit’s processing power in one direction or the other. @jamesh may be able to lend a helping hand here 