Most Galvo amps use a split supply of +24/Ground/-24. A very few, very inexpensive, 20K PPS hobbyist grade Galvos use +/- 15V.
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It does not matter if it comes from a pair of supplies or a single supply with dual outputs. In the end you will need around 100 watts of power supply. You can measure the voltages going to your existing amplifier pair with a voltmeter.
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Steve