The (probably) official specs of the A20H, extracted and “validated” through google translate from a few different Chinese sources 2 years ago, before I bought my own unit :)
MAX POWER (RMS) balanced / unbalanced
16 ohm n/a / 1200mW
32 ohm 2400mW / 600mW
150 ohm 530mW / 133mW
300 ohm 266mW...