Grab yourself an old ATX power supply from an old pc, they output decent current and even old 250w units can supply as much as 25A on the 12v rail depending on how that 250w is configured.
to turn it on you connect the green wire to any ground wire ( black) and all the yellow wires output +12v.
I have an old ATX psu rated for 22A on the 12v rail supplying 2x Imax b6 chargers, 2x two way radios, a powerful 12v fan rated at 2.5A and have a xt60 on a lead for bench setups and also using my XT60 phone charger at my desk plus I also have screw down / banana posts for hooking up anything else 12v.
I can use everything at once while charging on both b6 chargers at 5A each
With no issues.
The great thing about ATX power supplies is they will shut down if they sense a short instead of just continuing to pump power and will save your equipment which is particularly useful if your testing a new wiring setup on a model.
they also have over current protection and will shut down if you try and pull too much from them instead of burning out but you won't come close to the 12v limits of an ATX psu on just one b6 charger.
i regularly run both my b6 chargers at their max 5A current charging multiple packs on balance boards.
In the pic, the 9v displayed on the xt60 phone charger you can see is not the voltage it's getting, it's the voltage it's charging my phone at, the ATX psu outputs 12v.