Depending on how many batteries you wanna charge at once 12-15 volts will be fine! The Turnigy Mega 400w 20amps is the best bang for the buck at 12volts
https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=23590(Only available to U.S custmers only).You'll be able to charge up to 260ish watts safely on 12v, and you can parallel charge 4 5000mah 3s packs at 1c! I parallel charge 2 2s 5000mah batteries in about 30min at a 2c charge maybe less depending on how much I have to put back in! If you want a really good PS for cheap check out the($20) DPS600pb server PS! It's 575watts and 47a at 12volts, and really easy and safe to convert! I run 2 in series at 24volts for the PL8, it takes a little more work for safety but once done you'll never really want/need more power unless you field charge with a generator! Mostly the 12s and 14s heli guys will charge over 1000w at 3-4c etc for 15min charges to get on, because flight time usually last between 4-10min depending on setup, and flying style! Google the DPS600pb and how to convert, it's super easy! Hope this helps!
Here's a good basic/simplified link on how to convert the DPS600pb PSU:
https://sites.google.com/site/tjinguytech/my-projects/HP47A note: Most people connect pins 6,8,10.I'm not sure why he uses 6,9,10 but it works!I recommend 6,8,10. The super simple way to make the connection is to just find an old servo wire pull the 3 pins and snip the wires,twist them together, plug them into to 6,8,10,and voila you have a 12v 47a/ 575watt power supply. You can shrink wrap them,or just use 1Futaba/Hitec plug for each pin.