So I was messing with my hitec x2 400 charger and found some features I didn't know about, capacity cutoff, cell voltages etc, my question is I noticed my capacity cutoff was at 5000mah, my current lipos are 6900mah, does this mean even though it charges to 8.40v that the charger only put in 5000mah?

Itll stop charging at 5000mah. I have mine off. Along with the timer.

You mentioned cell voltages, not familiar with your charger but my powerlab let's me set voltage cut and I set it to 4.19v per cell.
Most cheap chargers (not saying yours is) over charge packs and that's bad for them.
Just gives that little buffer for safety's sake and the 0.2v will never be missed on the track.

It shows me the voltage of each cell which is cool cause I always wondered if my packs were balanced proper with the charger, but yes I watched it yesterday and both cells finished charge at 4.19, I'll check today to see if I could set it to not overcharge but I'm pretty sure it always finishes at that

That's good. My old turnigy would end charge at 4.23 or so. Lipo's with drop down to 4.2 in a few minutes, I just don't like pushing past 4.2.

1 more ? About my charger, it's 800watts total and 40amps total between the 2ports, my powersupply is 12.15v/47amps/575watts max, will I be stressing or possibly even fry the powersupply or charger if I charged both ports on 20amps so a total of 40amps

V x A = W
So you should be using about 1/2 of your power supplys max watt rating for a 2 cell per channel.

Even if your charger was still pushing 20a per channel as it neared 8.4v which I won't you would be at 336 watts for both channes. But you will never see that as it lowers amperage as it nears the end of the charge.

At the start of your charge where you will see 20a, let's say your pack was not used all the way and it was at 7v. You are using 140w on that channel.

Near the end you will be at 20a at say 8.2v which would be 328 for both channels in use and then it will start pulling amperage down as the voltage goes higher.

4 cell packs, you will need to limit amperage to not over do the wattage. Even nominal 14.8v @ 20a is 296 per channel and 592 for both.

You want to use about 80% of your power supply. Maybe 90% but I like to be nice to them and not stress them.

Thanks man