The i780 is the European version of the i907. It came out several months earlier but physically is virtually identical (the only real difference is the i907 has added the US 3G phone bands). So, any accessory for teh i780 should work for the i907.
The i907 has Samsung's S-20 connector. I believe (90% confidence) that the Blackjack II also has the same connector but that the original Blackjack does not. Easiest way to verify is to look up accessories on the Samsung site that work for the i907 and cross reference the model numbers of the other phones that also work with the accessory. Once you determine a specific Samsung model shares the S-20 connector you can order with confidence.
Blackjack 2 chargers work. I verified it after reading online that it is the same connector. Although in hindsight, I could have messed up the phone because stuff online isn't always accurate. But it DOES fit and charge exactly the same and I haven't blown up the phone so I guess what I read was right.