I am using a Samsung laptop 19V 4.74A AC Adapter Charger:
At 6.3V, it is capable of putting out a little over 14A, which should be more than adequate to run two 6AS7's. So if you are not able to get your desktop PS working, you might want to consider something like this.
Edit: I have run a single 5998 in my LD1+ with a 5A regulator. If the 5998 required 3 times 2.5A, or 7.5A, at start-up, I suspect my regulator would have failed. Based on my experience, I believe that anything over 2 times the rated amperage is probably fine for 6AS7-type tubes: 2399, 421A, 5998, 6080, 7802, 7236....
Edit2: The LD has a 1A heater circuit for drivers and 2.5A for powers. Two EF91's draw .6A, a bit more than half of LD"s 1A capacity. And two 6N30P draw around 1.7A, again more than half of the LD's 2.5A capacity.
So I believe that designing your heater PS circuit to handle 3 times normal operating current is perhaps a good thing to do, it is not necessary.
Edited by gibosi - 7/4/14 at 10:17am