Short answer: your power supply should work - you just need the right voltage, current rating, polarity, and connector.

An unregulated power supply is a kind of power supply whose output voltage varies with current draw. In other words, it does not put out a constant voltage - it is only rated to supply a minimum voltage at a certain current draw. In this case, you will need a power supply that can provide 9V DC at 700mA. Because most devices require a constant voltage, you can always use a higher rated supply.

If you test an unregulated power supply with a multimeter, you will likely see the voltage is higher than what is on the label, say 9.5V DC. That is because the multimeter is not putting a heavy load on the power supply. As the current draw increases, the supply voltage will drop. That is why you can use a higher rated device, but not a lower one.

In your post you said it uses a 3.7mm plug, but the manual link says 3.5mm with a positive tip. I assume that it means it uses a 3.5mm phone connector for power, like what you would see on a pair of wired headphones. The important part is that the positive 9V is connected to the tip, and ground on the sleeve. Sometimes, reversing these connections can damage devices, but there is usually a protection circuit inside that prevents this, and I would wager that this is no exception.

1A might be too much. You’ll also need to ensure the polarity is correct. There should be a label, usually co-located with the serial number, which states the input and polarity requirements of the DC plug.

I believe that the “unregulated” part means that it is not picky about voltage and the circuit can handle variations in voltages.

Have you put a multimeter on the power supply to confirm what voltage it is producing?

Amps are how much you can push Volts are how hard you can push

If you push too much, the device won't use everything If you push too hard, something is likely to break!

That's how I try to remember. It's a bit more complicated because you're not wasting 1.3a if it's only using 0.7. and I'd have to do the math but for example in some cases you could use (for example without checking math) 10v power supply and only use .6 amps

In your case go with what agentsac is saying, but I don't think you need to worry about max amps.

Oh wauw that was my first home pc… good memories :) cool buy!