I checked the line 6 power supply faq that there's an alternative to a [9VAC 1200mA minimum] power supply.

it said
"PX-2 AC: (Stomp modelers, All PODs, XT, and X3 series, XPS, Micro Spider): Output: 9v AC, 2000mA. The center pin diameter is 2.5mm.
Line 6 power supplies are available at you local dealer or at our Online Store.
Note: The Stomp Box Modelers will also work under DC (Direct Current) at 12V, 500 mA minimum. The center pin is positive (yes, center pin is positive as opposed to the DC-1 power supply)."

but then i checked flatliner that

"The Line 6 modelling pedals can be powered through the 9VDC (MM4, FM4) or 12VDC (DM4,DL4) outputs. Since these effects draw more current (150-185 mA) than average you can connect one effect with one output. The FLATLINER can power several Line 6 effects simultanously. Note: Line 6 modelling effects have reversed polarity. Use the right cable."

9VDC and 12VDC? O__o wtf

I think all they are saying is that for models MM4 and FM4 you use a 9 volt DC adapter and for models DM4 and DL4 you would use a 12 volt DC adapter. I am assuming the Flatliner can run both 9 and 12 volt outputs.

However, the POD series MFX are a bit different. They model lots of stuff and there for have a higher milliAmp requirement (ie 1,200 and 2,000 mA) There is a reason the alternative they gave you is 2,000 mA. I am assuming you are asking about a POD but your real question is a bit vague.

I would ask at the line6.com forums to be sure.