folks. looking at using this epay chinesium dc dc converter for portable operation.  does anyone have experience with using these as far as quality, receiver noise, etc

I haven't used that particular one but like most, the seller doesn't have a clue and the specs are nonsense.  No way will you ever get 900 watts out of that thing.    In general,  you can have something near the specified voltage but not at the specified current or power.  Even his own load tester shows 142 watts output and I wouldn't want t put my finger on the heatsink at that level for very long!   The only way to know what it's capable of is to buy one and test it or find someone else who knows their stuff that has done so.

The more common type can be found by searching "ZVS  45-390V" - they are now selling for < $5 shipped and work well as long as you derate them and provide sufficient filtering/shielding for your application.   The schematic of this design is also available as are replacement parts  and it's been around long enough to have become a "standard" that is available from numerous sellers.   The switching frequency is 75 kHz and I run the output voltage no higher than 300V, where they will supply up to 20 watts.   Be sure to bypass the supply leads if you're using them to run a transmitter as RF will definitely kill the controller IC.

73, Bob W9RAN