I have the venom pro2 and I use it to charge a 4s 7400 battery and since it has a 50 watt power supply it stops around 3.3 amps. I just recently wired the charger up to a 280 watt computer power supply thinking I could get more amperage out of the charger, but it still charges at 3.3 amps. Should I be getting the full 6 amps running DC or is the charger limited to 50 watts no matter how it's being powered?

Looking in the manual, this charger seems to stay at 50W of charge, no matter which supply you use.

That charger is rated at 7 amps and 80 watts. If you hit either limit, you can't get more out of it. Your problem is the 4S battery. That is about 16 volts in round numbers. 80 watts / 16volts = 5 amps. If you have the 50 Watt version, 50/16= 3.12 amps.

That is a big 4S battery. If you want to charge at 2C (about 30 minutes to charge from empty) you need 14.8 amps. The power required is 14.8 amps * 16 volts = 236 watts. At 3C you need 22amps and 355 Watts. You should be looking at something like a 500 Watts system. Like this for example:
https://www.progressiverc.com/the-su...00w-combo.html

I have had an i306B for years paired with a 1000 Watt supply (The Solution combo) but I mostly only use it for helicopter batteries (6S 5000's). For most everything else, I have been using this:
https://www.amainhobbies.com/protek-...k-8519/p578442
It is 200 Watts per side so at 4S the current is limited to about 12 amps. That is a little over 2C for my 4S 5000. For your 4S 7400, it would be about 1.6C or 35 minutes so ok but a bit under powered.

Thanks for the suggestions on some chargers you guys use, but at the time I can't afford to buy one. The Pro2 was alright as I only had a 2s and a few nimh batteries but now I have a Kraton and 4s lipos. A charger will definitely be next thing I buy. The 4s takes way too long to charge.