[AngelicaDeAlquezar]

While it's a fact that the printer is working, the subjunctive comes from my personal opinion that it's a good thing.
- Es muy triste que no quieras venir. - I find your presence pleasant, so I'm sad that you don't want to be with me.
- Es importante que hables varios idiomas. - I personally value people who speak several languages.
- Es horrible que uses esos zapatos. - I hate those shoes, so I think you shouldn't wear them.

As for "It'd be good if that printer were working", Poli's translation is fine.
Also: "Sería bueno que esa impresora estuviera funcionando".
In this case, my mood would improve if the machine were working, but the conditional is expressing that it is not.
- Sería conveniente que me dijeras qué regalo quieres. - You haven't told me what present you want, but I prefer you did.
- Sería terrible que aumentaran los impuestos. - I fear taxes could get higher, but they haven't yet.

In all these cases, the construction is the same:

Impersonal "ser" + adjective + "que" + subjunctive

- Es necesario que termines el trabajo.
- Era difícil que ganara mi equipo.
- Fue amable que me trajeras a casa.
- Será mejor que no compres un perro.
- Sería injusto que me culparan del robo.