Question

What type of transformer can I use to convert 12v dc to 120v ac with 5-8A output? step-up, step-down?

Answer 1

Note that, the transformer shold not be operated on DC supply. If we apply DC Supply to the transformer then its winding will be burn. because there is no rate change of flux linkages in the primary winding(DC is constant magnitude) ,Due to this no primary induced emf in the winding , and no opposition to the supply voltage ,hence transformer takes very high amount of current from the supply., and winding will be damaged.

IF you want convert 12v dc to 120v., first convert the 12v dc to ac voltage using inverter and then use step up transfomer. The step up transformer will increses the input voltage.it is a low voltage transformer so use shell type step up transformer.