Powering and operating dual electric linear actuators
You want to buy a switching power supply with a 12V output capable of at least 6A if you want to be able to operate both struts at the same time under full load.  The amount of current drawn will depend on how much force is pushing against each strut.  If you only need to operate one strut at once, then a 3A supply will probably do.

You could, in the simplest case, wire them directly in parallel.  However, it is unlikely that they will move synchronously unless they are directly bolted together, e.g. if there's one at each end of the desk they may become misaligned and jam or break the desk.  If one is under more load, it will move a little slower.  So probably you want a separate switch for each strut so that they can be controlled individually.

You will also need some means of reversing the polarity in order to change the direction of travel.  The usual means is a DPDT switch or relay; you can google up a schematic pretty easily.

If you buy switches rated for at least 3A (one strut) or 6A (both struts) then those switches can directly control the motor current.  More likely is that you might buy smaller/cheaper switches which actuate the coils of large (10A) relays, which are responsible for enabling and reversing the power.

Edit: you might want to look into building your desk so that it has a single central strut to perform the lifting work, supported by stabilising arms/scissors/whatever at each side of the desk.  That way, there are no alignment issues and no need to synchronise two struts.  If your lifting geometry results in more than 150kg load on the single strut, you could probably put the two right next to each other and they would be mechanically synced and provide up to 300kg of support together.