I did a pretty rigorous test the other day to measure the output of power supply beams. I did not calculate exactly how much they were drawing, but I had 2890 power supply modules drawing 'roughly' 900,000 power and they transferred ~90 power per second only. It took 2890 of them precisely 766 seconds to fill up a 200 million battery on a test ship that had no power generation of it's own. The consumption figure of 300 power sounds right. The output? Not even close.
Yeah this is true, I tested a similar thing myself with my own battery design and got the same result. I can share the blueprint with you if you'd like lancake.
Did both of you use logic to fire these power supply beams? I assume Planr at least did since that's about a battery/reactor design. There is/was a bug where logic beam duration was always fixed to 2.5 seconds when fired with logic. The attempt to fix it worked for normal beams but not for it support/slave ones, I believe a second commit was done to fix that but there were also a few more issues that were left unattended:
http://phab.starma.de/T46
I would like to see a blueprint of that planr, PM me it if you don't want it to be publically shared.
I checked your numbers panpiper and they seem off. You say these transferred 90 power per second only, so how did you they fill up 200 000 000 power in 766 seconds which is 261 000 per second, or 130 000 per tick?
Your 2890 power supply should supply 138 720 per second and consume 173 400 per second.