The datasheet gives the +-Vdc and the |+Vdc| + |-Vdc| values, both in specification and in the plots/graphs. (mod X = |X|)

The transformer voltage can be converted to DC voltage using this formula.

DCvoltage ~ Mains supply voltage / Rated Input voltage * rated output voltage * 1+regulation * sqrt(2) +-manufacturing tolerance - Vdrop of rectifier.

For worst case maximum voltage in the UK where we have a 240Vac supply with limits of 216 to 254Vac a 230:25+25Vac transformer with 7% regulation passing through one bridge rectifier

Max DC voltage = 254 / 230 * 50 * 1.07 * 1.414 - 1.0 +-tolerance ~ 82.5V+-tol

The dual polarity voltage will be ~+-41Vdc. Maximum worst case DC voltage is just inside the 84V limit for a 3886 chipamp. This is too high for a 6ohm and for a 4ohm speaker.

english correction:

it is written in the datasheet?

should be:

is it written in the datasheet?