I own a Hagerman Trumpet MC as well. Outstanding gear. For kicks, I tried running my low output (.35v) MC cart at 68db gain. Pretty quiet...no hum or noise. Try that level of gain with any phono stage with a wall wart. I currently like running it at 64db gain and it's perfect.
The Advantage of the setting loading and gain in the Hagerman is that these are all front panel mounted controls. So easy to do that you can help trying all the settings to find the best result.
My previous phono stage was the top of the line Project Phono box RS. Even with an outboard power supply, there was some hum at 60db gain.There was also a very slight hum running MM.
The Hagerman Trumpet MC has a very smooth, detailed and organic presentation. No hum, no noise. All with a wall wart. Not sure that an outboard power supply is necessary.