In my previous (very old) video I described a way to eliminate AC hum from the phono stage by connecting a wire from the pre-amp's body directly to the Earth pin of a mains plug. That video is here:
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In this video I've explained 2 more options, which I'll summarise here:

1) Get an earthed linear power supply. Note that not all linear power supplies are earthed. You can find loads of these on AliExpress and there are pictures of their internals. Make sure there is an earth wire connecting the AC C13 inlet to the transformer and metal body of the PSU. This in turn means that the Negative terminal of the DC power output is also earthed. This in turn earths your pre-amp and elimiates AC hum.

Note: Pro-Ject High Power it is an earthed linear power supply but it outputs 15 Volts only so it can't be used to power the Phono Box or any other Pro-Ject pre-amplifiers.

2) As demonstrated in this video, hook up an earthed audio appliance to your system. In my case the only earthed device is the old CD Transport tucked away in the cabinet below the amplifier. Thankfully this 'Little Dot CDP_I' has built in earthed PSU which means the whole unit is now earthed. I've connected this to my amplifier (with built in DAC) via Coaxial TOSLINK instead of optical, which means the whole audio system is now earthed through the CD Transport, this is because the body of the amplifier is now earth and so is all its RCA connectors. This in turn earths the external DAC above it and the Pro-Ject phono box in the left cabinet as well.

There is absolutely no AC hum in this setup.

UPDATE: On newer turntables e.g. Debut Carbon EVO, the ground lug on the phono output is connected to the negative (-) terminal of the DC motor. This means the whole system can be earthed by using a linear power supply e.g. Pro-Ject High Power it to power the motor.

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