if you are going 3s 8000 and you want to charge at 1C then you need at least 100W (most people suggest to overestimate by 20%) so you need at least 120W to be safe, at 12V (what most power supplies output to you would need a 10A continuous, so a 15-20A PS (if you go with a 13.8A supply you would need a minimum of 9A but 12-20A to be safe.
If you go up to 4S you would want to be closer to 18-20A+ power supply.