You have a 400w now? Me too. My plan is to upgrade to 600w and 6" ventilation like you... I will also be buying a 6" air cooled hood. My sun hut tent is 5' x 3' I will be running my 400w too. I want to get a dual lamp reflector like this
growzilla and do 600w hps and 400w mh in flower. There are a lot of good reflectors on that site btw. Like this
8" dual lamp raptor you would need 8" to 6" duct reducers... it's 2.5 x 3.5 There is a
6" single lamp version the same size for a little cheaper.
If you just want to run a single 600w in your current tent, the blockbuster is a good/popular choice. One thing you may get with cheap hoods is the air seal around the glass leaks and you have to find a way to seal it. Another option is the budget no-bullshit move and pick up a
cooltube with a big reflector. This one is 2' x 2'
Probably look into digital ballasts... Pretty much all of them are mh/hps switchable and dimmable. I don't have one but they are supposed to be slightly quieter and slightly cooler. Some claim even slightly more efficient. One thing you have to watch out for is shitty shielding causing RF interference with your neighbors' cable if you live in an apartment or something. Cable company will check it out if people complain, but I've only seen a couple threads about this possibility. I think you may have to buy HID bulbs designed for digital ballasts, but I am not sure about that.
Lumatek is good for name brand ballast... iPower and Apollo (amazon/ebay) for cheapy.
Also... yea upgrading from 400w to 600w is a good investment. Lumens per watt they are more efficient than 1000w hps and they smoke 400w. Running a 600w hps and mh in a dual lamp reflector would be the best in a tent my size I think... but I just want to run a 400w MH in flower so I don't feel like I wasted my money. Add some T5 side lighting and a couple reptisun 10.0 uvb cfls and that would be a pretty bitchin tent if you can keep temps down.
As for the plug, I think there are 2 kinds...
one is like this adapter; this is the type mine has. idk about the other kind.