This is a condensed summary of a useful but very long YouTube video, the link to which is at the bottom.
Four types of plasterboard fixing were tested. Here are the resulting weights held when a single one of each type was used to secure the top of a shelf bracket.
Cast aluminium screw-in, 12p (pack of 100) Screwfix, less than 10 kg.
Fischer UX6, 6p (pack of 100) Screwfix – 12.5 kg.
Gripit, 52p (pack of 25) Screwfix – 20 kg.
Spring toggle, 45p (pack of 20) Screwfix – 22.5 kg.
Easyfix Hollow Wall Anchors, 13p (pack of 100) Screwfix – 22.5 kg.
Note that a Rawlplug version is 30p each.
On another YouTube video a variety of plasterboard fixings were demonstrated by a different method to the above. The results are below, but there is a pattern evident. There are fittings which are strong: wall anchors, spring toggles, etc. These are twice as strong as fixings that are weak: metal plasterboard screws, pretty much all the ones that get a good grip of a reasonable area of the back of the plasterboard are pretty similarly strong, but only 2 or perhaps 3 times the strength of those things that are obviously much weaker.
GeeFix £2.23 each Total failure weight in 12.5mm plasterboard was 125KG or 275Lbs Hollow wall anchors £0.50 each Total failure weight 109KG or 240Lbs Snap toggles £1.30 each Total failure weight 129KG or 284Lbs Blue GripIt £0.83 each Total failure weight 101KG or 222Lbs Snap toggles £1.30 each Total failure weight 129KG or 284Lbs Spring Toggles £0.54 each Total failure weight 176KG or 387Lbs Metal plasterboard screw £0.37 each Total failure weight 53KG or 116Lbs
Use the UX6 and put twice as many in. That gets you greater strength than any of the others for a price almost identical to the cheapest.
My own experience is that standard Rawlplugs, either the 6 mm or 7 mm provide quite a strong fixing in plasterboard provided that you drill a very clean hole with a normal twist drill (not a masonry drill because these give a more ragged hole). At 2p a time for the brown ones they are hard to beat but I am not aware of any strength tests.