For the 1.12.2 Energy Converters I could find I found these two:
https://www.curseforge.com/minecraft/mc-mods/modernconverter (supports: RF, Tesla, Forge Energy, BuildCraft MJ, Refined Storage apparently??)
https://www.curseforge.com/minecraft/mc-mods/energy-converters (same as the other as well as recipe support for the mods)
Some mods do the MFR like converting I think which is LightningCraft for RF/Tesla/and it's own Power API but if you want EU, RF, Tesla and others I'd say go with any of the two above, that or Mekanism also might do the same as the MFR ones as it has support for it's own Power API KJ and all the major Power APIs (RF, Tesla, EU) but you do need to install the mod itself which is very big with all it's machines, utilities, ores and so on besides having the core parts/Power API installed. Although most mods that have their own Power APIs like LightningCraft, Planttech for example are niche and don't have converters but I assume most mods in your pack will have EU or RF/T so you shouldn't have any issues.
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