DI water would be the cheapest way to go. But if you are going to do it do it right. Get yourself a zinc anode and make sure it is in the water with it. Also you will need 3 types of filters .45 micron , a MIXED bed and a oxygen filter. With all that it will be good to go. I know this because...
here is what you do. You need to take the leads of the end voltage of the pwr supply and attach them to a external circuit card, then on that card you will need have have a step up transformer with the proper impedance matching. Then from the transformer but in a varible resister so you can...
What I suggest you do is get a voltmeter or better yet a multimeter and go ahead and check the leads of the PSU for the right voltage. Then go ahead and check the leads for OMH resistance and make sure that none of them are shorting to ground. You can usually pick up a cheap on a radio shack for...