Total N00b question about a plugpack

You won't get a 'less clunky' version - it's a 9V AC output which will have to be derived from a 'clunky' old mains transformer even if it's a 120V AC input version.

Such wall warts should be available but won't be too common.

What you could do is check out the input circuitry of the synthesizer to see how that 9V AC is being used. I suspect (needs confirmation) that it will feed a bridge rectifier to deliver a DC supply internally. If this is the case you could probably replace the 9VAC adapter with a DC output power pack (the internal bridge rectifier will sort out the polarity issue).

But this needs proper confirmation - post a picture of the innards of the synth, around the power plug and associated circuitry.

 

Well despite your link only being to page 1 of the schematic (the PSU part is on page 5) I did find it... bad news though. The synth uses a split-rail 9V supply internally and this is derived either from batteries or through that AC wall wart you have but there's no way the split-rail can be made from a fixed single-rail DC input.

In other words, to get that synth working on a power pack you WILL have to find one that delivers 9V AC at a minimum of 1A (more is ok).

 

No, that's a DC (unregulated) output.

The 'bar' with the 'dotted line' under is the give away.

 

Finding an AC output adapter isn't very easy at all. You may find it simpler to purchase a small transformer and mount it in a box.

Here's a picture of the ONE AND ONLY adapter with an AC output that I spotted on eBay.... the key part to note is the "9V~" bit. Far too many adapters are stated to be 'AC' but their output is actually DC so care needs to be taken to ensure you get the right type.



Small AC transformers are easier to find like these:

https://www.ebay.co.uk/itm/3W-5W-9W...hash=item28276a9fb8:m:mbZKABbkuQ7K34hXt7fG2LA

but since I'm searching the UK site they are all for 240V - searching the US eBay site will give 115V primary transformers (I presume) and you want one with at least 10VA (the VA rating is simply the voltage multiplied by the amperage, in your case 9V @1A = 9VA, rounded up to 10VA).