It doesn't sound like the gentleman is a great do-it-yourselfer when it comes to electrical things, so I personally think his best option is get a cheap 120v - 12v converter that he can plug into the wall then hook to his pump without any other equipment needed.
But for you guys that ARE handy with electrical things, if you are wanting a good cheap power supply to replace a battery or make a good and powerful electroplating outfit, a good solution is an old power supply out of a desktop pc!
The 12V rails will provide a 150 watts or so in even the cheapest power supplies. This amounts to around 12 amps @ 12v approximately. Don't forget however that most pumps that say 12V mean BATTERY 12V which is actually around 13.8V, while the PC power supply is an ACTUAL 12V. So at 12V your pump might put out a small % less than it's maximum rating.
There are several bundles of wires coming out of the power supply. All the red wires are 5V and all the yellow wires are 12V. Simply cut off the connectors and bundle them together. All the black wires are ground (or -) if you are thinking of a battery.
Well you plug it in and put your device on it and hit the power switch on the back of it and ... nothing happens... lol.
Power supplies from a pc do not work unless they get a power good signal. That signal is supplied on the one lone green wire in the large bundle of wires that connect to the motherboard.
To make it kick on simply take the 1 green wire and wire it to any black wire! That's it.
I use a pc power supply for my electroplating. Works wonderfully. Basic electrical knowledge, skill and tools are all that is required. Have a happy day