UKC

I'm looking for an Outdoor / robust / waterproof Solar Power Bank at a reasonable budget. There's plenty of cheap ones online but don't want to buy a crap one that doesn't work. So any recommendations and advice would be appreciated. I'm heading to Africa for a month which is the main use / need for the power bank. Thanks in advance for any advice....

You need to state what you're going to be charging. e.g. just mobile phones, or laptops?

Mobile phone & iPod

I recommend a powerbank and a seperate solar panel. Never seen a good combination; mostly tiny panels that barely charge anything.

In most cases; get a big panel and a decent powerbank. Less then 7 watt is a waste of time. A long cable can be handy on hot days, so you can hide the powerbank in the shade. Hidding the powerbank underneed a solar panel can still overhead it and the safety kicks in a prevent any charging. 

Personally I prefer a cheaper/older style power bank as the newer ones with fast charging capability, do exactly that. I prefer a slow charge and try to keep my batteries between 20-80%, so they last longer.

A few people in my club have got the 21W Anker solar charger (link below) and I've got one myself. It works well and seems relatively robust. One of us left the charger out in a passing shower without any ill effects.

https://www.amazon.co.uk/gp/product/B012VL20GW/ref=ppx_yo_dt_b_search_asin_...

All of us use our chargers in combination with a power bank. Anker do a few of these too. 

Charging a power bank is usually prefered, because some phones (iPhones usualy), when geting a lower current (the solar panel gets shaded temporarily by a cloud or trees) switch to trickle charge and remain in it until you unplug and plug them back (some more modern panels like the Anker or BigBlue 28W claim to be able to detect that and reset the current, although I am not sure if it really works consistently, from my experience). Of course, everything depends on the charging circuitry of the powerbank as well, if it can cope well with the varying current from the panel in changing conditions. 

When stationary (in camp), not only the power bank or phone should be in shade, it's important to try to have the solar panel itself somehow cooled (perhaps positioned such that there is some airflow underneath it, not just put it on hot ground). The (not so high to begin with) efficiency of photovoltaics gets quite lower when they heat up from all the sunlight.