First you set Vout unloaded. Then you put a DMM in series 10A scale current measuring mode between plus out PSU and active load's red binding post. Black post directly connected to zero out PSU. You turn the active load's pot until you read 4A. You will not be able to measure & trim Vout for long before the little board sinks get very hot at such high constant current so beware. You could start with setting less test current like 1A. To see output cables Vdrop also measure Vout at load side.
The fuse manufacturers in their recommendations don't specify transformers shape they just categorize by primary voltage and VA capability.
Up to 400VA for less than 600V primary voltage single phase transformers they say +300% their primary current for SLB fuse value.
Primary current is VA/VAC primary. From 500VA to 2kVA they relax the recommendation to +170%. For more huge they say +125%
Up to 400VA for less than 600V primary voltage single phase transformers they say +300% their primary current for SLB fuse value.
Primary current is VA/VAC primary. From 500VA to 2kVA they relax the recommendation to +170%. For more huge they say +125%