This is not an actual recommendation for a restaurant, but you will find good and value food anyway:

The Carrer Blai (Blai Street) is a very popular pedetrianized street in Poble Sec where you can find quite a number of pintxo bars and usually a great ambience. 

Pintxos are typical Spanish appetizers: a simple slice of white bread with different toppings. They are usually displayed on the counters of the bars, you get a plate, chose and pick them yourself and order your drinks with the staff. The prices in the restaurants in Carrer Blai are about 1,50€ per pintxo, some extravagant or warm ones might be a bit more expensive. Check out the variety and prices before sitting down - there are plenty of other bars.

Excellent place for bar- & pintxo-hopping!

- total on bill: 1,50€ per pintxo

CELLER CAL MARINO, in the very soul of Poble Sec is another excellent wine & tapas temple where old-established locals meet handsome hipsters. And they are all looking for the same thing: a glass of proper vermut and/or wine and a bite to eat. They do not just offer a variety of yummy homemade croquetas (e.g. sobrassada with honey, calçots or mushrooms with vermuth!) and Spanish/Canarian tapas but first and foremost serve local and national wines – bottled and to bottle.

The restaurant although quite spacey does not have a lot of tables (actually barrels) with stools to sit, but the spirit is to stand on the bar anyway.

Periodically the owners organise music or performance events in CAL MARINO where local bands and performers entertain you while slurping your delicate vermuth. http://www.calmarino.com/

ABIRRADERO is a brewpub, a bar which makes and sells their very own craftbeer.

The great majority of their beers are brewed in Catalunya and around half of them in a manufactury just around the corner: the 'Instituto de Cerveca Artesana' I.C.A. in the very same neighborhood of Poblesec.

You can choose between 40 different beers, all freshly tapped from the shooters. These make the ABIRRADERO the brewpub with the biggest variety of tapped beers in Europe. The constantly changing offer is displayed on a digital screen just behind the counter.

If you enter as lost as I, concerning the science of beer and brewing industry the friendly waiters will recommend you different options and even give you try before you decide weather to take a half or a whole pint. 

The inside of the ABIRRADERO is rather light and simple. They also offer some snacks and tapas but I did not try any  yet.

The beers cost between 3-4€ (half a pint) up to 5-7€ for a whole pint.