Partial answers ...
On voltage, current, power and energy. To the best of my knowledge, EnergyPlus only reports on power (W), and consequently on energy (J), for the vast majority of its "energy-consuming" object classes. Exceptions would be generators (e.g. PV) and transformers - AHUs wouldn't normally fall in that category.
Many similarly-named output variables can be reported either in W or in J. One can either request both W and J output variable variants, or post-process J from (i) reported W and (ii) defined timestep duration (e.g. 5 min = 300 s). I usually only request time series data in W, and do my post-processing from there (e.g. to tally GJ).
If ones postulates that a RTU operates at 240 V, then one can isolate current from P = I x V. I know, that's very basic. But for the purposes of building energy simulation, fixed voltage (e.g. 240 V) seems like a reasonable assumption.
On missing output variables. An EnergyPlus-generated run/eplusout.rdd file contains all admissible output variables, specific to your IDF. So if what you're after isn't there, then you're out of luck. You know what objects you're interested in, so the best is to search (e.g. CTRL-F) known keywords in the .rdd file.
It looks like your model is a variant of the US DOE Prototype SmallOffice model, and so I tested this with another variant of the SmallOffice I keep in some of my repositories (like this one). As with your model, I requested all (557) possible output variables (listed in the OpenStudio Application), and enabled the following (just in case):
OS:Output:Diagnostics,
{fd2b9480-2f48-497a-96c6-b7ed055c5b05}, !- Handle
DisplayAdvancedReportVariables; !- Key 1
As expected, around 200 requested output variables weren’t generated by EnergyPlus (as reported in the run/eplusout.err file). This is expected for the vast majority of reported failures: for instance, any requested variables on fuels (e.g. diesel) or fluids (e.g. steam) will fail if these are not present in the model (fair enough).
Yet a few failures seemed odd to me. I filed an EnergyPlus issue, and a similar OpenStudio issue, on (now) unavailable output variables. Not sure if any of the variables you're looking into fall in some similar situation.
Hope this helps.
