Reported on the RC Bugs forum. The MFE cart does not receive power when placed under an Energy Loader. Batbox and CESU carts load/unload successfully. I've confirmed in Creative and Survival modes using Railcraft_1.7.10-9.3.3.6 and industrialcraft-2-2.2.653-experimental.

You need to install a Transformer upgrade.

That should have been obvious, I suppose. Didn't think about it. Thank you for the update.