Agreed, many of the Tosh chassis seems a bit flexible, but you can usually get replacement parts for them, as you can for Dell / HP / Samsung / Compaq
They've got the scale to put in long production runs and keep spares.
The likes of ASUS / Acer (and its subsidiaries) get most of theirs done in contract design & build knocking shops called "ODMs" (original design manufacturers) who make to a price, have short runs, and don't keep spares. If you're lucky ASUS might have 5% overrun for spares, but then you'll find one distributor (e.g. Dixons are good at this) will buy the lot and no-one else gets a look-in. Only source of spares then is through the second-hand Steptoes on Ebay.
The Dell desktop - I assume its a small form factor one? If so, yes they use bespoke low-wattage power supplies, totally non-standard. If I get one of those in for repair I usually rebuild it into a standard sized case, for which power units are easy. Dell full sized towers are OK, all the parts in there are easy to replace.
And as a rule Dells, both laptop and tower, are close to indestructible in normal use.