Sadly, 800mA won't cut it. You need 9VAC at 1.2 or 1A from memory. I never like to load up power supplies at anywhere over 75% of their rated capacity for constant current draw. 800mA powering a 1.2A device would either just shut the power supply down, or kill it quickly.
And for testing if it is AC or DC, it might show a symbol.
~ means AC and one with a flat line on the bottom and 3 dashes on top means DC. You could also find out with a multimeter if it can test both AC and DC.
Amiga 4000: Apollo Turbo 040, 128MB Fast, 40gb HDD, CD-ROM (needs internet)
C64: 1541U-II, MixSID, WiFi, LumaFix64
ZX Spec, A1200, CD32, MacPlus/SE, A500, BBC Turbo Master (NASA), 2600, Acorn 4000, VIC-20, IBM 5155, GameBoy