Powerstream are probably the only company making them in the US although there are a couple of one-man shops selling similar products for the ham radio
I'd check with Dell directly about the power requirement of the display, I suspect it is really 12V and the converter they supply is putting out 14V under no load but dropping closer to 12 when connected.
If you tried to build a 12->14 VDC buckbooster yourself, it would cost more in component parts
than the powerstream unit. I have heard one complaint from one user that the Powerstream created a lot of RFI, which might affect navigation equipment
underway, but I don't know if that was one defective unit or a larger problem. The folks at Powerstream are good at answering the phone
though, they could probably tell you.
The voltage for an LCD monitor has to be your typical "electronics quality" DC. If your GPS
, computer, etc. are happy with it, it is good enough. If it runs too high or too low, or has a lot of AC mixed in, that's the only real problem.