300 amp 12vdc power supply on a standard(American) wall outlet
100A at 12V is about as much as you can get from a 15A outlet. That means you'd have to allow a lot of recovery time (hours, not minutes).

If the 240VAC outlet/hard-wired is an option, you could consider simply connecting a couple Meanwell RSP2400-12 166A supplies (or similar) in parallel. No mussing with batteries, then, and you'll get (just) the 300A you require.