Questions about Burl gear.

Hey Gearspace folk.
Iam contemplating on going the burl route for my converters.
I track with great vintage microphones and preamps and have used apollos for my console and mics, for mixing and recording.
I always saw my converters as my studiogears weak link.

But i have some questions as i want to buy used Burl gear.

1.
What is the differences between Burl revisions if you want a used burl. Is there a desired revision or revisions not to get?

2. Why did burl change the powersupply from bp250 to bp300.

Thanks for reading anyhow.
Kind regards Bob