The chargers that have integrated power supplies have limitations because you can only have so big a PS inside the case design. Most I have seen with built in supplies have a 10 amp max charge rate, and that is only for the 1-3s batteries, maybe 4S max. The power available is no different, just one method uses a supply internal to the charger and one external. In fact, an external one may be more efficient and or better quality.

the pros of having the supply internal to the charger... convenience of plugging in one unit.
the cons... if the supply goes bad, you lose everything. you are limited by the internal supply to available power.

if you go with an external supply, you can select proper voltages for optimal operation. You can get a large one and use multiple chargers on it. You can upgrade your charger and keep using the same supply for years and years. They are super cheap to make yourself! Chargers are cheaper without built in supplies. Chargers without built in supplies can have higher charge amperage. High quality supplies from servers are relatively cheap and if you build one yourself will give you good, regulated output for multiple chargers for not much $$. You can easily build them for $20 each or less for a 40+ amp 12V supply

-just ordered the 400w Duo from SKy RC., but you can get a PL6 or PL8 for awesome fast charging. Don't forget newer batteries can take super high charge currents. my new Nano-techs can do 10C charging.