Due to EU regs for energy saving it is no longer possible to buy or sell a 5 V USB power supply.
There are some manufacturers who can still build a high quality switch mode power supply with good RF filtering.
For my own use to power antenna amplifiers and to replace all the cheap tat passed off as phone and tablet USB chargersI I've replaced them all with TT Electronics SW4479B 5 V 2.1 A USB chargers. This is designed for UK use with the 3 pin plug. It was originally designed to meet the high reliability (MTBF of 50000 hours) specification so it's a well made quality item. It appears to be RF quiet with no noticeable conducted RF on the mains supply or USB cable. If you put a receiver and antenna up against the charger there is some RF noise very close in within a few inches.
I bought mine from Rapid Electronics part number 85-2892, the current price is £6-89 + VAT.
TT Electronics probably make versions for other electrical supply sockets but I've not checked yet.