The problem is something else: on the iMac 21.5 inch slate 2012, the RAM is not easily accessible but soldered. In addition, the iMac must be cut open and the adhesive residues removed and replaced with new ones.
Your notebook uses DDR3L (Low Voltage) RAM, so i'd suggest buying that instead of normal DDR3 RAM. The following product should be compatible (obviously not tested myself), but it's according the specs provided: HyperX Impact (2x, 8GB, DDR3L-1600 (PC3-12800), SODIMM 204)
Yes, the Rams fit, even if Apple claims that this model can only take 8 GB. But: Please don't expect too much from very much RAM in the MacBook - if the machine feels slow, first and foremost replace the hard drive with an SSD.
It would be good if you could give me the link to check. But basically it is not the same product (there is an L hidden in the middle of the manufacturer's no.). The product with the L is low-voltage 1.35V and the product without the L is 1.5V. It is quite possible that Digitec does not offer the product in the low-voltage version.
Perhaps there is a product from Corsair that is available at Digitec: http://www.corsair.com/de-de...
DDR-1600 could work in iMac mid 2011 (but only at DDR-1333 speed).
Looks like there is no guarantee for ValueRAM in Macs. It does work in my 2012 mini (DDR-1600).
If it does not work in your iMac, then can you return the opened package or try it in another machine?