KO servo power problem

[MRD]

Ive got a KO PDS-2344FET servo running from a micro spektrum powered by a Nosram brushless ESC and had no problems at all but now I'm running a 20t motor I want to swap to a normal brushed esc. The problem is that Ive tried two different Mtronics esc's and an LRP runner reverse and with all three the servo is glitching and sometimes it cuts out the spektrum altogether.

Ive tried a speky power cap but this only helps a little bit. I was looking at getting an LRP IPC3.1 but it may have the same power delivery problem. Ive got an Orion Vortex servo and regardless of the ESC it still works fine. Anyone got any Ideas why the KO is such a power zapper and how I can get round this? Cheers