At the very end of the Fusion section of the section of Mekanism Advanced, there is an ambiguous power supply check for "50M". Cannot be clicked on. Does not trigger for 50MFE+ stored in reactor or elsewhere. Some blogs from previous versions denote using the FTB Questblock, which is deactivated in JEI.

Quest does not provide the info, but Tracking Screen is required, attached to any power supply.