1200mA will work just fine, the SC-55 will only draw what it needs and the PSU will provide that. It's the other way around that won't work: 500mA PSU and 1200mA device.
Getting a higher voltage reading on these old unregulated PSUs without load is perfectly fine, if you measure it connected to the SC-55 when it's powered on you'll get 9v.
ACI/ACB are just models, no need to worry about that.
The only thing you need to worry is correct polarity (SC-55 needs negative on the center) and that your PSU provides enough mA to the device.

In theory, a linear type power supply would give higher volts when loaded under the rated current. I think many of these older power bricks are linear. The gear can take a bit of overvolting, though, I expect.

The SC-55 really uses a 7805 to power it's electronics so it can take more than 9v - max is 24v or something IIRC. The only issue is the heat and the included heatsink is designed to work around 9v ratings.
The higher voltage reading with no load is perfectly normal on unregulated PSUs.

keropi wrote:

The SC-55 really uses a 7805 to power it's electronics so it can take more than 9v - max is 24v or something IIRC. The only issue is the heat and the included heatsink is designed to work around 9v ratings.
The higher voltage reading with no load is perfectly normal on unregulated PSUs.

Actually it has 16V bulk capacitors and both 5V and 8V LDO regulators. So 9V is minimum safe value it will work reliably and maximum short term safe value is somewhat below 16V. I would not go much over 12V-13V for a few reasons. First of all the rating is 9V so that should be used in the long term. Capacitors also like when the voltage over them is somewhat less than the rating printed on them, at least in extreme temperature or ripple conditions (these extremes won't apply here though). And any extra voltage is just converted to heat in the linear regulators.

firage wrote:

In theory, a linear type power supply would give higher volts when loaded under the rated current. I think many of these older power bricks are linear. The gear can take a bit of overvolting, though, I expect.

Only when the linear power supply is unregulated. Regulated ones would output exactly what it says on the supply.

GabrielKnight123 wrote:

the adapter I got with it has on the power supply sticker "9V DC 1200mA" and on the back of the SC55 it says it needs 9V 500mA the guy I bought it from said the power supply was from something else so will the higher 1200mA be safe with the SC55's 500mA?

I am quite sure the the power supply is unregulated so the voltage drops when connected to SC-55. The 12.5V it outputs unloaded is also fine. So it should be safe to use.

Ofcourse I wasn't suggesting one should use a 24v PSU 🤣 , just what the 7805 could take as max. I did not think of the rest of the components being rated lower than 16v TBH, my train of thought stopped on the 7805 heatsink that won't like the extra heat once you go pass the 10+ v mark ... 🤣

Of course 😀

Anyway, I gave this some more thought and 9VAC RMS voltage has a 12.7V peak voltage, which does match the about 12.5VDC the OP measured when some things are taken into consideration. As firage mentioned, transformer output voltages are specified under load, and so the voltage is higher when there is no load. And there are the rectifying diodes that have a slight voltage drop when there is no load, but have more drop when there is some load. Most likely the Roland AC adapter just contains full wave diode bridge and rectifying capacitor.

Ah good thanks everyone I'm glad I have a good to use adapter, when I first got the adapter it was not working so I opened it and my first thought was the fuse was kaput but it was just the cable where people wrap it around the plastic arm near the input for power on the SC55 or the guy before me who had it put the cable at a bad angle, Jepael there is 4 diodes and a capacitor and the cap looked to be in good condition but the makers of the adapter used sticky tape to "hold" the pcb to the transformer but most of the sticking force is from the two wires off the transformer power output soldered to the board I had to un-solder the pcb from the transformer to look for defects and I used the same high technological sticky tape to keep it in place, would a transformer get hot enough to burn sticky tape that is wrapped around it?